Effects of Methods Used For Blood Collection on Plasma Concentrations of Luteinising Hormone,Testosterone, And Cortisol In Male Dogs

Summary

The effects of two putative stressors relative to the collection of blood, namely the environment of the treatment room and the pain associated with venepuncture, on plasma levels of luteinising hormone (LH), testosterone and cortisol were examined in six trained male experimental dogs. Blood samples were collected from the dogs in a treatment room as well as in the kennels (control), and by venepuncture as well as via an indwelling’ intravenous catheter (control). No significant influence of either stressor on plasma levels of LH, testosterone or cortisol was found Plasma concentrations of these hormones varied considerably both between and within dogs. Mean (± SEM; n = 6) plasma concentrations were 4.3 ± 1.0 μg/l for LH, 4.6 ± 1.9 nmol/l for testosterone and 68 ± 10 nmol/l for cortisol It was concluded that the putative stressors, the environment of the treatment room and the pain associated with venepuncture, did not significantly influence plasma levels of LH, testosterone or cortisol in trained male experimental dogs.     

Salivary cortisol as a stress parameter in piglets]

The relationship between salivary and plasma levels of total and free cortisol was monitored in 97 male piglets, aged two to four weeks, subjected to castration. Samples were taken 10 minutes before (basal value) as well as one, two, three, four and 24 hours post castration and at the same time intervals from a control group of 17 animals which did not undergo surgery. Simultaneously to blood (indwelling catheter) withdrawing saliva was collected by two cotton swabs. Cortisol levels were measured by radioimmunoassay (RIA). A highly significant increase in total, free and salivary cortisol was found within the first four hours after castration compared to the control group. The percentage increase one hour after castration above basal values was highest in free plasma cortisol (21.08 +/- 2.03 nmol/l vs. 61.26 +/- 4.16 nmol/l; 290.6%), and lowest in total plasma cortisol (177.33 +/- 9.69 nmol/l vs. 374.09 +/- 18.21 nmol/l; 211.0%), whereas salivary cortisol showed an 255.7% increase (10.46 +/- 1.03 nmol/l vs. 26.75 +/- 1.93 nmol/l). Total cortisol included 11.9-16.4% free cortisol. Salivary cortisol concentration was between 5.9% and 7.5% of the total plasma cortisol concentration. The highest correlation between total plasma cortisol and salivary cortisol occurred one hour after castration (r = 0.57; p < 0.01). The correlation between free and salivary cortisol was lowest for basal values (r = 0.27; p < 0.05), whereas correlations for the remaining time points were highly significant (0.41 < or = r < or = 0.61; p < 0.01). For the control group significant correlations were found between salivary and total plasma cortisol (0.58 < or = r < or = 0.89; p < 0.05) and between free and salivary cortisol (0.63 < or = r < or = 0.92; p < 0.05). The present work indicates that the measurement of salivary levels of cortisol reflects the concentration of this hormone in plasma samples of piglets.     

Plasma free cortisol concentrations in dogs with hyperadrenocorticism.

Unbound or free cortisol constitutes a small fraction of total plasma cortisol, but is believed to represent the biologically active portion of this circulating glucocorticoid. We tested the hypothesis that the percentage free cortisol was altered in plasma from dogs with hyperadrenocorticism, which could account for a greater target tissue response to this circulating hormone. The percentage free cortisol in plasma samples from human beings, healthy dogs, and dogs with hyperadrenocorticism was estimated, using centrifugal ultrafiltration-dialysis. Total cortisol concentrations were determined by use of radioimmunoassay. Total cortisol concentrations appeared greater in plasma from human beings than in plasma from either group of dogs. However, the percentage free cortisol was lower in plasma from human beings, resulting in a calculated concentration of free cortisol that was quite similar between plasma from human beings and healthy dogs. Total plasma cortisol concentrations were greater (P less than 0.01) in samples from dogs with hyperadrenocorticism (190 +/- 113 nmol/L; mean +/- SD) than in healthy dogs (102 +/- 85 nmol/L), but the percentage free cortisol was not different between these 2 groups (dogs with hyperadrenocorticism, 16 +/- 9%; healthy dogs, 13 +/- 6%). However, plasma free cortisol concentrations (product of total and the percentage of free cortisol) were greater (P less than 0.01) in samples from dogs with hyperadrenocorticism (36 +/- 41 nmol/L) than in those from healthy dogs (16 +/- 9 nmol/L). Significant (P less than 0.001) positive linear relationships were found between total cortisol concentrations and percentage free cortisol in plasma samples from healthy dogs and dogs with hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)     

EFFECT OF STRESS ON STEROID HORMONE LEVELS IN RACEHORSES

SUMMARY Cortisol and testosterone were measured by radioimmunoassay in plasma samples from race horses. None of 6 stressed male horses had Iow cortisol levels but testosterone levels (0.81 ± 0.15 nmol/l) were significantly lower than in healthy horses (1.86 ± 0.31 nmol/l). The conclusion was made that adrenocortical insufficiency is not a common association of stress in race horses. The reduction in testosterone levels is probably a nonspecific response similar to that seen in other species.     

Relationships of gonadotropins, testosterone, and cortisol in response to GnRH and GnRH antagonist in boars selected for high and low follicle-stimulating hormone levels

Considerable variation exists in the serum levels of gonadotropins in boars; this results in differential testicular function. Boars (Chinese Meishan, European White composite, and crosses of the two breeds) selected for high and low circulating FSH concentrations were used to define possible differences in pituitary sensitivity to GnRH and GnRH antagonist and gonadal and adrenal responses. After a 2-h pretreatment sampling period, boars were injected with GnRH or GnRH antagonist and repetitively sampled via jugular cannula for changes in serum concentrations of FSH, LH, testosterone, and cortisol. In response to varying doses of GnRH or GnRH antagonist, FSH, LH, or testosterone changes were not different in high- or low-FSH boars. Declines in LH after GnRH stimulation were consistently faster in boars selected for high FSH. Chinese Meishan boars had considerably higher cortisol concentrations than White composite boars (132.2 +/- 28.5 vs 67.4 +/- 26.8 ng/mL, respectively; P < .01). When select high- and low-gonadotropin Meishan:White composite crossbreds were sampled, cortisol levels were elevated but comparable between the two groups (126.5 +/- 13.7 vs 131.4 +/- 13.4 ng/mL, respectively). After GnRH antagonist lowered LH concentrations, administration of hCG resulted in increased testosterone and cortisol concentrations. Although testosterone concentrations remained high for 30 h, cortisol concentrations returned to normal levels within 10 h after hCG injection. The mechanism by which boars selected for high gonadotropins achieve increased levels of LH and FSH may not be due to differences in pituitary sensitivity to GnRH but to differences in clearance from the circulation.     

Concentrations of carnitine in the seminal fluid of normospermic, vasectomized, and castrated dogs

Concentrations of total carnitine (free and esterified) were determined in seminal fluids from 12 normospermic dogs before treatment and from the same 12 dogs after assignment to control, vasectomized, or castrated treatment groups (4 dogs each). Before treatment, the mean concentration (+/- SD) of carnitine in seminal fluid was 946 +/- 345 nmol/ml and was not significantly different (P greater than 0.05) among groups on any seminal collection day. After surgery, mean concentrations of carnitine in seminal fluid from vasectomized and castrated dogs were 49 +/- 9 and 14 +/- 5 nmol/ml, respectively and were lower (P less than 0.001) than the mean concentration in control (sexually intact) dogs. Dogs with obstructive azoospermia may be distinguished from those with aspermatogenesis (secretory azoospermia) by measuring seminal carnitine concentration. Seemingly, the epididymis is the major source of carnitine in canine seminal fluid, because the concentration of carnitine in prostatic fluid was only 58 +/- 53 nmol/ml, whereas the concentration of carnitine in 6 pools of epididymal fluid was 18.8 +/- 3.9 mumol/ml.     

Changes in the level of plasma cortisol, progesterone and total testosterone in developing hairless dogs.

Changes in the levels of plasma cortisol, progesterone and total testosterone were examined in developing hairless and haired dogs. Cortisol levels in the hairless dogs seemed to be higher than those in haired dogs within the age of 4-5 weeks. No apparent changes were seen in the level of plasma progesterone between the groups of hairless females and haired females. Total testosterone levels in hairless males showed to be significantly lower than those in haired males at the age of 13-21 weeks.     

Effect of African trypanosomiasis on plasma cortisol and thyroxine concentration in goats

Changes in plasma cortisol and thyroxine (T4) levels were measured weekly in female goats experimentally infected with Trypanosoma congolense. Values for plasma cortisol (range 10 to 25 nmol litre-1) and T4 (range 65 to 120 nmol litre-1) were within normal ranges in all goats before infection and in control animals throughout the 24 weeks of study. Cortisol/T4 ratios of 0.23 to 0.15 (or 1:4 to 1:7) were obtained. In the infected goats a significant increase in cortisol and decline in T4 were simultaneously observed within one week of the onset of parasitaemia and fever. A peak cortisol/T4 ratio of 2.0 (2:1) was obtained four weeks after infection when cortisol levels rose to 59.0 +/- 8.9 nmol litre-1 and T4 declined to 29.4 +/- 2.2 nmol litre-1. Thereafter the mean levels fluctuated but remained high (over 30 nmol litre-1) for cortisol and low (under 50 nmol litre-1) for T4 up to 18 weeks after infection. Both hormones tended to return to normal levels towards the end of the study. The changes in mean cortisol levels showed a significant inverse correlation with changes in T4 (r = -0.57, P less than 0.001, n = 26). It is suggested that in trypanosomiasis, hypothalamic stress causes increases in plasma cortisol levels and at the same time suppresses the activity of the thyroid gland.     

Level of plasma testosterone in relation to age, gonad size and sexual libido in bulls

The level of plasma testosterone (PT) was determined by the direct RIA method with tritium-labelled testosterone. An average level of 2.25 +/- 1.46 nmol PT/l was found in 57 bullocks old 47 to 106 days. Until the age of 67 days, the level of PT was 1.11 +/- 0.69 nmol/l and from the 68th to the 110th day 2.74 +/- 1.32 nmol. In the period from the 7th to the 13th month of age, 108 bulls were found to have the PT level of 23.04 +/- 19.81 nmol/l, which was a statistically significant increase (P = 0.01) as compared with the prepubertal period. In 154 bulls old two years and older, the PT level was found to be 21.72 +/- 14.78 nmol/l. In comparison with bulls old 7 to 13 months, no statistically significant difference was recorded in PT levels. Neither was found any correlation between the gonad size and PT level and any relation between libido and PT level. In the bulls having no libido the PT level was insignificantly higher than in the bulls with pronounced libido sexualis. In all the studied groups of bulls, a comparatively high variation was found in PT values.     

Plasma testosterone and LH responses to LHRH in double-muscled bulls treated with trenbolone acetate and zeranol

Twenty-four double-muscled Belgian White Blue bulls were assigned, according to body weight, to two groups with and without treatment with anabolic agents. Implants containing 140 mg trenbolone and 36 mg zeranol (Forplix) were inserted sc on the upper face of the ear flap. Plasma concentrations of testosterone and luteinizing hormone (LH) were determined at d 0, 30 and 60 of the experimental period. Mean testosterone levels at d 0 for treated and controls were, respectively, 2.1 and 1.7 ng/ml during the 10-h sampling period. At d 30 and 60, testosterone levels were strongly depressed in implanted bulls (.2 ng/ml) as compared with 2.5 and 1.7 ng/ml in control bulls (P less than .001 at d 30 and P less than .01 at d 60). Average plasma LH concentrations were identical in the two groups at d 0 and 60 (1.1 and 1.5 ng/ml, respectively), but showed a slight decrease at d 30 in the treated group (P less than .10). The pulsatile character of LH and testosterone profiles was abolished by the Forplix treatment. Luteinizing hormone-releasing hormone (LHRH) injection at d 0 was followed in both groups by an immediate and sharp increase in plasma LH concentrations. The LH response reached a maximal value between 20 to 40 min postinjection and then declined rapidly. On the contrary, Forplix treatment strongly reduced LH and testosterone responses to LHRH stimulation in treated animals. Average daily gain and feed to gain ratios were 1.087 +/- .127 and 7.52 +/- .32 kg, respectively, for the control bulls and 1.335 +/- .092 and 6.24 +/- .24 kg for the Forplix-treated bulls, thus clearly showing a beneficial effect of Forplix treatment.     

Stress responses in adult cattle due to surgical dehorning using three different types of anaesthesia

Dehorning adult cattle is a surgical procedure causing distress of varying intensities that can be reflected in behavioural changes and alterations in plasma cortisol levels. Stress responses during the dehorning process were evaluated in 18 Red Pied cows. The cows were divided into 3 groups of six and kept in tie-stall housing. Those in the first group were dehorned under general anaesthesia (GA) induced by intravenous administration of xylazine and ketamine. The second group was dehorned under sedation and local anaesthesia (SLA) induced by intramuscular administration of xylazine and local anaesthesia with lidocaine. The third group was dehorned under local anaesthesia (LA) with lidocaine. Dehorning was performed with a foetotomy wire. Blood samples were taken 0.5 h before dehorning to determine cortisol levels, and, by means of a central venous catheter inserted into the jugular vein, during surgery at 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7 and 8 h post-surgery. Concurrently, occurrence of stress behaviours was assessed. Cortisol levels were measured by enzyme immunoassay (EIA). The lowest mean peak levels of plasma cortisol (82.53 +/- 6.04 nmol l(-1)), the most rapid return of plasma cortisol levels to baseline values (1.92 +/- 1.11 h), and the lowest occurrence of stress behaviours (2.38 +/- 5.83%) were noted in the SLA group. The highest mean peak levels plasma cortisol (113.86 +/- 25.65 nmol l(-1)), the slowest return of plasma cortisol levels to baseline values (3.83 +/- 2.18 h) and the most frequent occurrence of stress behaviours (65.48 +/- 28.72%) were observed in the LA group. There were significant differences between the SLA and LA groups in peak plasma cortisol levels (p = 0.011) and in occurrence of stress behaviours (p = 0.003). Sedation induced by intramuscular administration of xylazine in conjunction with local anaesthesia with lidocaine is considered the most suitable method of anaesthesia when dehorning adult cattle. Local anaesthesia with lidocaine alone was least suitable.     

Alteration of reproductive hormone levels in pregnant sows induced by repeated ACTH application and its possible influence on pre- and post-natal hormone secretion of piglets

Prenatal stress has been seen as a reason for reproductive failures in pig offspring mostly originated or mediated by changed maternal functions. Experiments were conducted in pregnant gilts (n=32) to characterize effects of elevated maternal glucocorticoids on the secretion of reproductive hormones (LH, progesterone) during the 1st (EXP 1), 2nd (EXP 2) and 3rd (EXP 3) trimester of pregnancy (TP). Transiently elevated cortisol release was repeatedly achieved by application of 100 IU adenocorticotropic hormone (ACTH) (Synacthen Depot) six times every second day beginning either on day 28 (EXP 1), day 49 (EXP 2) or day 75 of pregnancy (EXP 3). Glucocorticoid concentrations were examined in umbilical blood vessels of fetuses which mothers were subjected to ACTH at 2nd and 3rd TP (EXP 4). Furthermore, the pituitary function of newborn piglets of EXP 2 was checked by a LH-RH challenge test. In sows, LH concentrations were at low basal level (0.1-0.2 ng/ml) but with pulsatory release pattern during each TP. The number of LH pulses/6 h (LSM +/- SE) of saline treated Controls increased with ongoing pregnancy and decreased to the 3rd TP (1.3 +/- 0.2 in EXP 1 vs. 2.0 +/- 0.1 in EXP 2 vs. 1.4 +/- 0.1 in EXP 3, p<0.05). After ACTH treatment the number of LH pulses left unchanged in Experiments 1 and 2 (1.3 +/- 0.2 and 1.5 +/- 0.1) and decreased in EXP 3 (0.8 +/- 0.2, p<0.05). Differences (p<0.05) were obtained comparing the LH pulse number of ACTH and saline treated sows at the 2nd and 3rd TP. Moreover, areas under the curve (AUC) of each LH pulse and of LH over baseline were significantly reduced by treatment. Levels of progesterone increased (p<0.05) for 150 to 170 min after each ACTH application both in EXP 1 and EXP 2, but not in EXP 3. The mean progesterone concentration was different between trimesters, and ACTH and Controls (1st TP: 30.0 +/- 0.9 and 24.4 +/- 0.7 ng/ml; 2nd TP: 35.5 +/- 0.9 and 29.1 +/- 1.0 ng/ml; 3rd TP: 13.6 +/- 0.2 and 13.1 +/- 0.1 ng/ml; p<0.05). In fetuses (n=87) recovered 3 h after ACTH or saline (EXP 4), the plasma cortisol concentrations were significantly increased in umbilical vein (93.7 +/- 5.5 vs. 47.0 +/- 5.3 nmol/l) and artery (95.7 +/- 5.4 vs. 66.4 +/- 5.4 nmol/l), and in periphery (46.8 +/- 5.3 vs. 27.1 +/- 5.3 nmol/l) compared to controls. Plasma ACTH concentrations, however, did not differ in fetuses of both treatment groups. Postnatal LH-RH challenge tests (1st and 28th day post partum) induced LH surges in female piglets (n=67) both of ACTH and saline treated sows, but did not differ between groups (1st day: 7.2 +/- 0.8 vs. 8.1 +/- 0.7 ng/ml; 28th day: 10.5 +/- 1.7 vs. 13.6 +/- 2.2 ng/ml). However, basal LH of piglets whose mothers were submitted to ACTH during 2nd TP was lower on 1st day (1.7 +/- 0.2 vs. 2.3 +/- 0.2 ng/ml, p<0.05) but not on 28th day (1.0 +/- 0.2 vs. 1.1 +/- 0.2 ng/ml). However in both groups, the basal LH was always higher on 1st as on 28th day (p<0.05). Thus, chronic intermittent ACTH administration is able to influence the release pattern of maternal reproductive hormones. However, these findings demonstrate that these effects are dependent on the stage of pregnancy. Furthermore, it was shown that maternal cortisol can cross the placenta during gestation and thus may affect maternal-fetal interactions and, as a result, reproductive function of offspring.     

Influence of sexual stimulation and the administration of human chorionic gonadotrophin on plasma testosterone levels in dogs

The influence of sexual stimulation and human chorionic gonadotrophin (hCG) administration on plasma testosterone concentrations was assessed in five male Beagles. Each dog was exposed to three experimental treatments: C treatment (Control, no stimulation), hCG treatment (dogs were SC injected with 1000 IU of hCG) and sexually stimulated (SS) treatment where semen was collected from the males. All dogs were exposed to all treatments, one per week for three consecutive weeks, with a 1 week of rest between treatments. Blood samples were taken with the same time intervals (0, 10, 30, 60 and 120 min) relative to treatments. Plasma testosterone concentrations were determined with a solid-phase I(125) radioimmunoassay. In the control treatment, the testosterone plasma levels did not show significant changes throughout the tested period (mean values ranging between 2.8 and 4.7 ng/ml); the hCG group presented a significant increase (p < 0.05) in plasma testosterone levels 30 min after hCG administration and had the highest value (8.7 ng/ml) at 120 min post-hCG. Finally, the SS group revealed a slight reduction in testosterone concentration immediately after ejaculation, but the values remained nearly unaltered until 120 min after semen collection. When the groups were compared, the hCG group showed higher plasma testosterone values (p < 0.05) than did the C and SS groups, starting at 30 min and continuing until the end of sampling. This study demonstrates that sexual stimulation associated with semen collection does not produce transitory modifications in plasma testosterone concentrations.     

Adrenal response to the low dose ACTH stimulation test and the cortisol-to-adrenocorticotrophic hormone ratio in canine babesiosis

This prospective, interventional, case-controlled study sought to determine the association between adrenocortical function and mortality in dogs with naturally occurring Babesia rossi babesiosis. Sixty-eight dogs with canine babesiosis were studied and fifteen normal dogs were used as controls. Blood samples were obtained from the jugular vein in each dog prior to treatment, at admission to hospital, for the measurement of basal plasma ACTH (adrenocorticotrophic hormone) and serum cortisol concentrations. Immediately thereafter, each dog was injected intravenously with 5 microg/kg of ACTH (tetracosactrin). A second blood sample was taken 1h later for serum ACTH-stimulated cortisol measurement and the resultant calculation of delta cortisol by subtracting basal from ACTH-stimulated cortisol. Diagnosis of babesiosis was confirmed by polymerase chain reaction (PCR) and reverse line blot (RLB). Three outcomes were defined: hospitalization with subsequent death (n=4); hospitalization followed by recovery (n=48); and treatment as an outpatient (n=16). Basal cortisol, but not ACTH-stimulated cortisol, was significantly higher in patients compared to control dogs. Basal- and ACTH-stimulated serum cortisol concentrations were significantly higher in the dogs that died, compared to hospitalized dogs that survived and compared to dogs treated as outpatients. There was no significant difference in delta cortisol concentrations or cortisol to ACTH ratios across outcome groups in dogs suffering from B. rossi babesiosis However, dogs with delta cortisol concentrations below 83 nmol/l had significantly higher cortisol to ACTH ratios compared to dogs with delta cortisol concentrations above 83 nmol/l. These findings of increased basal- and ACTH-stimulated cortisol and increased cortisol to ACTH ratios confirm the absence of adrenal insufficiency and concur with those in human malaria.     

Effect of ACTH and CRH on plasma levels of cortisol and prostaglandin F2alpha metabolite in cycling gilts and castrated boars

The present study was designed to evaluate the effects of synthetic ACTH (1-24, tetracosactid) and porcine CRH on the plasma levels of cortisol and PGF2alpha metabolite in cycling gilts (n = 3) and castrated boars (n = 3). The experiments were designed as crossover studies for each gender separately. Each animal received, during three consecutive days; 1) ACTH (Synacthen Depot) at a dose of 10 microg/kg body weight in 5 ml physiological saline, 2) porcine CRH at a dose 0.6 microg/kg body weight in 5 ml physiological saline or 3) physiological saline (5 ml). The test substances were administered via an indwelling jugular cannula in randomized order according to a Latin square. The administration of ACTH to cycling gilts resulted in concomitant elevations of cortisol and PGF2alpha metabolite with peak levels reached at 70.0 +/- 10.0 and 33.3 +/- 6.7 min, respectively. Similarly, the administration of ACTH to castrated boars resulted in concomitant elevation of cortisol and PGF2alpha metabolite with peak levels reached at 60.0 +/- 0.0 and 20.0 +/- 0.0 min, respectively. Cortisol peaked at 20 min after administration of CRH in both cycling gilts and castrated boars with maximum levels of 149.3 +/- 16.5 nmol/l and 138.3 +/- 10.1 nmol/l, respectively. It can be concluded that administration of synthetic ACTH (tetracosactid) to pigs caused a concomitant elevation of cortisol and PGF2alpha metabolite levels in both cycling gilts as well as castrated boars. The administration of CRH to pigs resulted in an elevation of cortisol levels in both cycling gilts and castrated boars. Conversely, PGF2alpha metabolite levels were not influenced by the administration of CRH either in cycling gilts or in castrated boars.     

Effects of chronic gonadotropin-releasing hormone agonist treatment on serum luteinizing hormone and testosterone concentrations in boars.

Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH210), and serum luteinizing hormone (LH) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days -2 and -1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days -1, 0, 4, and 8. Serum testosterone and LH concentrations were determined by radioimmunoassay. Maximal LH (7 +/- 1 ng/ml) and testosterone (26 +/- 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, LH and testosterone concentrations decreased to pretreatment values (0.3 +/- 0.1 ng/ml and 1.8 +/- 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile LH release were observed between the groups. Testosterone and LH concentrations in samples collected at 6- and 12-hour intervals and pulsatile LH release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum LH and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in LH and testosterone concentrations in mature boars.     

Comparison of mitotane treatment for adrenal tumor versus pituitary-dependent hyperadrenocorticism in dogs.

The purpose of this study was to determine the sensitivity of dogs with hyperadrenocorticism to treatment with the adrenocorticolytic agent mitotane. Specifically, we looked for differences in response to treatment using this drug in dogs with adrenocortical tumors (adrenal tumor hyperadrenocorticism, ATH) vs those with pituitary-dependent hyperadrenocorticism (PDH). For inclusion in this study, each dog must have had clinical signs, data base laboratory abnormalities, and endocrine screening test results consistent with the diagnosis of hyperadrenocorticism. Further, each dog had to have been treated for at least 6 months with mitotane and have histologic evidence for adrenocortical or pituitary neoplasia (all dogs were necropsied). Thirteen dogs with ATH (8 carcinomas, 5 adenomas) were identified. The ages and body weights of these 13 dogs were computer-matched to 13 dogs with PDH. All dogs were initially treated with approximately 50 mg of mitotane/kg/d of body weight. Reexaminations were performed after 7, 30, 90, and 180 days of treatment. Individual dosages varied widely after the initial 5 to 12 days of treatment. The mean (+/- SD) dose of mitotane (mg/kg/d) for the first 7 days of treatment was 47.5 +/- 9.4 for dogs with ATH vs 45.7 +/- 11.9 for dogs with PDH. The mean plasma cortisol concentrations 1 hour after ACTH administration at the 7-day recheck were significantly higher in dogs with ATH (502 +/- 386 nmol/L) than in dogs with PDH (88 +/- 94 nmol/L).(ABSTRACT TRUNCATED AT 250 WORDS)     

The function of the pituitary-testicular axis in dogs prior to and following surgical or chemical castration with the GnRH-agonist deslorelin

Chemical castration, that is the reduction of circulating testosterone concentrations to castrate levels by administration of a GnRH-agonist implant, is a popular alternative to surgical castration in male dogs. Detailed information concerning the pituitary-testicular axis following administration of a GnRH-agonist implant is still scarce. Therefore, GnRH-stimulation tests were performed in male dogs, prior to and after surgical and chemical castration. This approach also allowed us to determine plasma concentrations of testosterone and oestradiol in intact male dogs for future reference and to directly compare the effects of surgical and chemical castration on the pituitary-testicular axis. In intact male dogs (n = 42) of different breeds GnRH administration induced increased plasma LH, FSH, oestradiol and testosterone concentrations. After surgical castration basal and GnRH-induced plasma FSH and LH concentrations increased pronouncedly. Additionally, basal and GnRH-induced plasma oestradiol and testosterone concentrations decreased after surgical castration. After chemical castration, with a slow-release implant containing the GnRH-agonist deslorelin, plasma LH and FSH concentrations were lower than prior to castration and lower compared with the same interval after surgical castration. Consequently, plasma oestradiol and testosterone concentrations were lowered to values similar to those after surgical castration. GnRH administration to the chemically castrated male dogs induced a significant increase in the plasma concentrations of LH, but not of FSH. In conclusion, after administration of the deslorelin implant, the plasma concentrations of oestradiol and testosterone did not differ significantly from the surgically castrated animals. After GnRH-stimulation, none of the dogs went to pre-treatment testosterone levels. However, at the moment of assessment at 4,4 months (mean 133 days ± SEM 4 days), the pituitary gonadotrophs were responsive to GnRH in implanted dogs. The increase of LH, but not of FSH, following GnRH administration indicates a differential regulation of the release of these gonadotrophins, which needs to be considered when GnRH-stimulation tests are performed in implanted dogs.     

Validation of a commercially available enzyme-linked immunosorbent assay (ELISA) for the determination of cortisol in canine plasma samples

Samples were obtained from clinically normal dogs before and after ACTH stimulation and dexamethasone suppression tests. The test kit Enzymun-Test (Boehringer Mannheim) for determining cortisol concentrations in human plasma was used in connection with the analyser system Enzymun-Test (Boehringer Mannheim) System ES300 following the manufacturer's instructions. The intra-assay and inter-assay coefficients of variation were 1.28% and 5.64%, respectively. The mean recovery when assaying samples with a cortisol content of more than 100 nmol/L was 95.41%, but this percentage decreased in samples with lower cortisol levels. The sensitivity of the assay was 2.76 nmol/L. The results of the ACTH stimulation and dexamethasone suppression tests were similar to those published previously. The ELISA method evaluated allows a precise and sensitive determination of cortisol concentrations in canine plasma samples. The major drawback observed was the loss of accuracy at low cortisol concentrations. Since the assay tends then to report lower cortisol concentrations, the generally accepted concentration of 40 nmol/L may not be suitable as the cutoff value in dexamethasone suppression tests.     

Salivary Cortisol Concentrations in Healthy Dogs and Dogs with Hypercortisolism

Background: Measurement of salivary cortisol is a useful diagnostic test for hypercortisolism (HC) in humans. Objectives: To determine whether measurement of salivary cortisol concentration is a practical alternative to plasma cortisol to diagnose HC, to validate the use of salivary cortisol, and to examine the effect of time of day and sampling location on salivary cortisol. Animals: Thirty healthy dogs and 6 dogs with HC. Methods: Prospective, observational clinical trial including healthy volunteer dogs and dogs newly diagnosed with HC. Salivary and plasma cortisol concentrations were measured with an immunoassay analyzer. Intra‐ and interassay variability, linearity, and correlation between salivary and plasma cortisol concentrations were determined. Results: The required 300 μL of saliva could not be obtained in 88/326 samples from healthy dogs and in 15/30 samples from dogs with HC. The intra‐assay variability for measurement of salivary cortisol was 5–17.7%, the interassay variability 8.5 and 17.3%, and the observed to expected ratio 89–125%. The correlation (r) between salivary and plasma cortisol was 0.98. The time of day and location of collection did not affect salivary cortisol concentrations. Dogs with HC had significantly higher salivary cortisol values than healthy dogs (10.2 ± 7.3 nmol/L versus 1.54 ± 0.97 nmol/L; P < .001). Conclusions and Clinical Importance: The ROCHE Elecsys immunoassay analyzer correctly measured salivary cortisol in dogs. However, a broad clinical application of the method seems limited, because of the large sample volume required.