Characterization of leptin binding in bovine kidney membranes

The interactions of leptin with its receptor and other leptin binding sites is not well described or understood. We have used Scatchard analysis of saturation binding data to characterize the affinity of leptin for binding sites in bovine kidney membranes. 125I-Leptin was used in saturation studies, over a range of concentrations from 50 pM to 9 nM. 125I-Leptin differentiated a high affinity binding site from an abundant low affinity site. The high affinity/low density binding site (putative leptin receptor) had K(d)=0.098 nM and B(max)=46.2f mol/mg protein. An additional class of low affinity, highly abundant sites with an apparent K(d)=175 nM, and B(max)=574 fmol/mg protein was characterized. The association and dissociation kinetics for 125I-leptin binding were also studied. Dissociation of the leptin-receptor complex was very rapid, and this necessitated the use of a specially developed separation method for radioligand binding studies (precipitation with PEG and filtration). Competitive displacement of 125I-leptin by mouse and human leptin and polyclonal anti-bovine leptin antibodies was dose-dependent. Specificity of binding was shown as bound 125I-leptin was not displaced by insulin or control antibodies. These data indicate that leptin binds the bovine leptin receptor with high affinity and that a pool of leptin is bound to abundant cell membrane-associated proteins. These observations are consistent with the plasma concentration range for leptin and imply that free leptin concentration in the tissues may be partially buffered by cell-associated and bound forms in plasma. Thus, acute changes in leptin secretion may have little effect at the leptin receptor. The development of leptin agonists/antagonists should facilitate further characterization of leptin binding and clarify the role of abundant low affinity binding sites at the leptin axis.     

Epidermal dexamethasone receptors in dogs with confirmed hyperadrenocorticalism, hypothyroidism or undiagnosed hormonal alopecia

Low capacity, high affinity [3H] dexamethasone binding receptors were identified in cytosolic preparations of the skin (mean number 42.0 +/- 25.2 fmol mg-1 protein, apparent dissociation constant (1 nM +/- 0.23) of clinically normal dogs. No [3H] dexamethasone binding was observed in the skin of nine out of 10 dogs with confirmed spontaneous hyperadrenocorticism or in the skin of three out of six dogs with undiagnosed hormonal alopecia. A reduction was detected in the number of [3H] dexamethasone binding receptors in the skin of one dog with confirmed hypothyroidism. This study provides evidence for the susceptibility of canine glucocorticoid receptors to down regulation by imbalances of endogenous hormones, particularly increased glucocorticoid concentrations.     

Estrogen receptor in bovine skeletal muscle

In connection with investigations of the anabolic action of estrogens, we examined skeletal muscle of veal calves for estradiol receptors. The high speed supernatant of muscle homogenate was incubated with .5 nM 3H-estradiol and for the determination of nonspecific binding with .5 nM 3H-estradiol plus 13 nM estradiol at 0 C overnight. After treatment with charcoal two times, the supernatant was analyzed by agar gel electrophoresis. Specific binding was found in the typical position of cytosolic estradiol receptor. Ninety percent of 3H-estradiol binding was suppressed by estradiol-17 beta, zeranol, estrone or diethylstilbestrol, but was not affected by testosterone, dihydrotestosterone, trenbolone or progesterone. The specific binding activity varied between .3 and 2.0 fmol/mg protein and the dissociation constant of the receptor was Kd = 60 pM. After an enrichment up to 42 fmol/mg cytosolic protein using heparin sepharose, the receptor remained unchanged as determined by agar gel electrophoresis. Although uterine tissue generally contains 1,000 times more estradiol receptors, these results clearly demonstrate that skeletal muscle also contains estradiol receptors with identical properties. This indicates that one possible component of the anabolic action of estrogens may be the direct stimulation of the muscle via the estradiol receptor.     

Characterization of porcine beta1- and beta2-adrenergic receptors in heart, skeletal muscle, and adipose tissue, and the identification of an atypical beta-adrenergic binding site

The objective of this study was to characterize porcine beta1- and beta2-adrenergic receptors (beta1-AR and beta2-AR) in heart, skeletal muscle, and adipose tissue by measuring the binding of a radioligand to cell membrane fragments. In skeletal muscle (LM), [3H]CGP12177 labeled a homogeneous population of beta2-AR as evidenced by the rank order of affinity of catecholamines [(-)isoproterenol > (-)epinephrine > (-)norepinephrine], a high affinity of the binding site for the beta2-AR-agonist clenbuterol (equilibrium dissociation constant, Kd = 16 nM), and a low affinity of the binding site for the beta1-AR-antagonist CGP20712A (Kd = 21 microM). The affinity of ICI118551, a ligand selective for beta2-AR in other species, was uncharacteristically low in porcine LM (Kd = 441 nM), but was consistent with a value reported for the cloned porcine beta2-AR. In heart ventricle, ligand binding revealed a predominant population of beta1-AR, judged by the rank order of affinity of catecholamines [(-)isoproterenol > (-)epinephrine > or = (-)norepinephrine] and high-affinity binding to CGP20712A (Kd = 40 nM). The Kd for ICI118551 (731 nM) was close to that observed at beta2-AR in LM, confirming that ICI118551 is not subtype-selective in the pig. Displacement studies using (-)propranolol, clenbuterol, and (-)isoproterenol revealed a second high-affinity binding site in the heart that was not a beta2-AR and could not be eliminated by guanosine 5'-triphosphate or guanylyli-midodiphosphate. In adipose tissue, an equal number of beta1- and beta2-AR was identified through the binding of clenbuterol and CGP20712A, whereas ICI118551 could not discriminate between these sites. In further experiments, we used 10 microM CGP20712A to eliminate beta1-AR binding and allow accurate Kd values to be determined at beta2-AR for nonselective ligands. Under these conditions, another binding site was observed that had a high affinity for (-)propranolol (Kd = 20 pM), which is inconsistent with beta3- or beta4-AR binding reported elsewhere. Our results indicate that porcine adipose tissue contains beta1-AR, beta2-AR, and an atypical binding site in the proportions 50, 34, and 16%, respectively, of the total binding sites labeled by [3H]CGP12177.     

Complex interaction of ergovaline with 5-HT2A, 5-HT1B/1D, and alpha1 receptors in isolated arteries of rat and guinea pig

Vascular effects of ergovaline mediated by 5-hydroxytryptamine(HT)2A, 5-HT1B/1D, and alpha1 receptors were studied in isolated arterial preparations of rat and guinea pig. In rat tail artery ergovaline behaved as a potent contractile partial agonist showing an agonist potency (pEC50) of 8.86 +/- 0.03, a maximum response (Emax) of 59 +/- 2% with respect to 5-HT, and a partial agonist affinity (pK(P)) of 8.51 +/- 0.06. Ergovaline was equipotent with ergotamine (pEC50, 8.69 +/- 0.07; Emax, 52 +/- 4%; pK(P), 8.36 +/- 0.11). Contractile responses to ergovaline and ergotamine were surmountably antagonized by the 5-HT2A receptor antagonist ketanserin (3 nM). Antagonist affinity (apparent pA2) for ketanserin against ergovaline and ergotamine was 9.19 +/- 0.08 and 9.36 +/- 0.17, respectively. Ergovaline showed extremely slow on-set and off-set kinetics in rat tail artery. The construction of cumulative concentration-response curves required about 4 h, and the contractile response to ergovaline (30 nM), which completely abolished the subsequent contractile response to 5-HT (10 nM to 1 mM), could not be reversed by wash-out. In guinea pig iliac artery moderately precontracted with prostaglandin F2alpha (0.05 to 0.5 microM) ergovaline behaved as an agonist (pEC50, 7.71 +/- 0.10) with a potency similar to that of 5-HT (pEC50, 7.60 +/- 0.05). The contractile response to ergovaline was inhibited by the 5-HT1B/1D receptor antagonist GR127935 (10 nM). The apparent pA2 value for GR127935 against ergovaline was 8.90 +/- 0.12. Ergovaline (10 nM) produced no contractile response in guinea pig iliac artery when added before the PGF2alpha-induced precontraction but caused insurmountable blockade of the contractile response to the 5-HT1B/1D receptor agonist 5-carboxamidotryptamine (5-CT). The apparent pA2 value for ergovaline against 5-CT was 8.56 +/- 0.18. In rat thoracic aorta ergovaline (2 microM) activated alpha1 adrenoceptors only with low efficacy (Emax, 12 +/- 3%) but surmountably antagonized norepinephrine-induced contractions with a pK(P) of 7.07 +/- 0.12. It is concluded that the powerful constrictor effect of ergovaline mediated by activation of vascular 5-HT2A and 5-HT1B/1D receptors may explain the vascular symptoms of fescue toxicosis observed in livestock grazing tall fescue pastures infected with the endophytic fungus Neotyphodium coenophialum.     

Changing adrenergic sensitivity of the caruncular arterial vasculature supplying the bovine placentome

With the advancement of gestation, blood flow increases preferentially to the caruncular bed of the gravid uterus in association with a decreasing sensitivity of the uterus to the vasoconstrictive effects of circulating catecholamines. This study directly compared the sensitivity of the caruncular artery (CA) of the isolated bovine placentome to phenylephrine (PE), a specific alpha 1-adrenergic receptor (AR) agonist, with that to norepinephrine (NE) and epinephrine (E), both of which are alpha 1-, alpha 2-, and beta-AR agonists, at two stages of gestation (140 to 170 d, mid-pregnant; 210 to 270 d, late pregnant). The CA of each placentome was perfused with oxygenated Krebs Ringer solution into which PE, NE or E were administered; increases in intra-arterial pressure were recorded. Further, NE content and numbers of alpha 1- and alpha 2-AR in the CA, intercaruncular arteries (ICA) and uterine arteries (UA) were quantitated. The CA from mid-pregnant cows exhibited greater (P less than .05) contractile responses to NE and E than did the CA from late pregnant cows, whereas responsiveness to PE remained constant. No difference in NE content, alpha 1-AR or alpha 2-AR numbers were observed in the UA, ICA or CA between mid-pregnant or late pregnant cows. Alpha 1-AR numbers were similar in CA, ICA and UA. However, CA contained threefold greater alpha 2-AR numbers than either the ICA or UA (50.2 +/- 6.1 vs 14.6 +/- 1.6 and 14.8 +/- 2.4 fmol/mg protein, respectively; P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Specific binding of naloxone to ovine brain tissue: comparison of brain regions and endocrine states

Binding of [3H]naloxone ([3H]NAL) to brain membranes was quantified by Scatchard analysis using two methods of separating bound from free [3H]NAL. In the centrifugation method, membranes that were soluble at 1,000 x g, but sedimented at 20,000 x g, were incubated with [3H]NAL. For filtration, all membranes that sedimented at 20,000 x g were incubated and filtered through glass filter fibers. Nonspecific binding was estimated using greater than 500-fold excess of unlabeled naloxone (10(-6) M). Specific binding of [3H]NAL was used to generate linear multiple-point Scatchard plots, which indicated a single class of high-affinity sites. In Exp. 1, 10 ovariectomized (OVX) ewes were injected with estradiol-17 beta alone or in combination with progesterone. Compared with OVX controls, these hormonal treatments did not affect binding of [3H]NAL (centrifugation method) to combined hypothalamus (HYP) + preoptic (POA) tissues. In cyclic ewes (Exp. 2, filtration method), affinity constants (2.4 +/- .2 x 10(8) M-1) did not differ among HYP, POA and basal forebrain (BF) tissues, but BF had more sites (39 +/- 3 fmol/mg) than either HYP (14 +/- 1) or POA (17 +/- 1). Binding affinity and concentration of sites within each brain area (HYP, POA, BF) did not differ between d 8 and d 16 (preovulatory but after luteolysis) in normally cycling ewes. Overall, neural tissue dissected from BF had a greater concentration of binding sites than HYP or POA. Exogenous and endogenous fluctuations in ovarian steroids did not affect binding of [3H]NAL to these tissues.     

LHRH receptor, LH and FSH concentrations in anterior pituitaries of cycling, noncycling and early pregnant heifers

In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of temperature and plane of nutrition on beta-adrenergic receptors in heart, kidney, and liver of lambs

We determined the effects of temperature and feed intake on beta-adrenergic receptors (beta-adrenoceptors) in tissues of sheep. Twenty-four lambs were exposed during three 5-wk periods to either thermoneutral, control (W; 23+/-2 degrees C) or cold (C; 0+/-2 degrees C) temperatures and were fed either ad libitum (A) or restricted (R) levels of feed intake, resulting in four treatment groups: WA, WR, CA, and CR. Hearts, kidneys, and livers were harvested at slaughter and binding of [3H]dihydroalprenolol to plasma membrane extracts was used to determine densities (B(MAX)) and binding affinities (Kd) of beta1 and beta2 adrenoceptors. The B(MAX) values ranged from 12.10 to 201.26 and 3.38 to 12.30 fmol/mg protein for beta1 and beta2 adrenoceptors, respectively; heart and kidney had the highest and lowest values, respectively. Feed restriction reduced (P < .05) beta1 and beta2 receptor densities in heart but increased (P < .05) beta1 receptor density in kidney and liver. Cold temperature exposure reduced beta1 receptor density in heart tissue during feed restriction. The Kd values, ranging from 1.32 to 5.98 nM, were increased (P < .05) by cold exposure and feed restriction in kidney and liver. Because the effectiveness of hormones is a function of their concentrations, binding affinities, and their receptor densities, these results imply that cold temperature exposure and feed restriction could potentially reduce (in heart) and increase (in kidney and liver) metabolic responsiveness of tissues to catecholamines.     

Interactions of xylazine and detomidine with alpha2-adrenoceptors in brain tissue from cattle,swine and rats

Xylazine is an alpha2-adrenoceptor agonist sedative with a much higher interspecies variability in effect than detomidine, another alpha2-agonist used in veterinary practice. In the present study, we have used radioligand binding in brain tissue to investigate if the high species variation in sensitivity to xylazine could be explained in terms of receptor interactions. Species known to be more (cattle) or less (swine and rats) sensitive to xylazine were used. There was no variation in the density or the subtype pattern of the alpha2-adrenoceptors that could explain the species variation recorded in vivo, as a homogenous population of the alpha2A/D-subtype (200-300 fmol/mg protein) was found in all species. The species differences in the affinities of xylazine and detomidine were minor and similar for the two drugs. The only parameter investigated where a significant species difference was found for xylazine but not for detomidine was the slope of the inhibition binding curve when the G-protein coupling was diminished. For xylazine this slope was considerably lower than unity (i.e. 0.77 +/- 0.075) using cattle preparations compared with 0.92 +/- 0.037 (mean +/- SE) and 0.90 +/- 0.028, respectively for swine and rats, while for detomidine this parameter was close to unity in all species (cattle, swine, rat). This finding indicates that the species variation in effect for xylazine could be due to differences at the G-protein level or further down-stream in the effect cascade.     

Expression of the porcine beta2-adrenergic receptor in Chinese hamster ovary cells

The gene for the porcine beta2-adrenergic receptor (pbeta2AR) was transfected into Chinese hamster ovary (CHO) cells for expression. Fourteen stable cell lines were obtained and exhibited receptor densities ranging from 12 to 2,371 fmol/mg membrane protein. The receptor density was not correlated with estimates of gene copy number obtained by Southern hybridization. The pbeta2AR in CHO cells exhibited saturable binding of [125I]CYP (Kd = 14.5 pM) and stereospecificity for (-)- and (+)-isoproterenol. The relative affinities for (-)-isoproterenol (ISO), (-)-epinephrine (EPI), and (-)-norepinephrine (NEPI) were ISO > EPI > NEPI, which are characteristic of beta2AR. The affinity values for these ligands were similar to those in other species. Binding of ISO, EPI, and NE revealed two affinity states of the betaAR; the high-affinity state was eliminated by adding Gpp(NH)p, a nonhydrolyzable GTP analogue. Binding of the antagonist propranolol modeled to only one affinity state, and Gpp(NH)p did not affect binding. Multiple affinity states are characteristic of agonist-induced coupling of betaAR with G-proteins, and the data suggest that the cloned pbetaAR is functionally competent. Data confirm that the pbeta2AR is the pig version of beta2AR. Stable CHO cell lines will be useful for characterization of pbeta2AR and screening and designing potential drugs that may be used to enhance pig production.     

Epidermal and hepatic glucocorticoid receptors in cats and dogs

Low capacity, high affinity [³H] dexamethasone binding receptors were identified in cytosolic preparations of liver (mean number 45±10·1 fmol mg⁻¹ protein, apparent dissociation constant 0·4±0·1 nM) and skin (mean number 46·4±23·8 fmol mg⁻¹ protein, apparent dissociation constant 1 ± 0·2 nM) of clinically normal dogs. For clinically normal cats, approximately half these numbers of receptors with a lower affinity, were detected in liver (mean number 23·1±10·4 fmol mg⁻¹ protein, apparent dissociation constant 3·2±0·9 nM) and skin (mean number 23·90±10·9 fmol mg⁻¹ protein, apparent dissociation constant 2·2±1·5 nM). This difference between dogs and cats in [³H] dexamethasone binding receptors may contribute to the relative glucocorticoid resistance observed in cats.     

Pharmacologic identification of putative D1 dopamine receptors in feline kidneys

The presence of dopamine (DA) receptors in feline kidneys is a matter of contention. Radioligand binding and Western blotting studies were employed to determine whether DA receptors are present in feline kidneys. The pharmacologic profile of the selective D1-receptor antagonist [3H]-SCH 23390 was studied in renal cortical membrane preparations from cats by conducting saturation binding isotherm and competitive binding experiments. [3H]-SCH 23390 bound to feline renal cortical membranes in a manner consistent with labeling of a D1-like receptor. The binding profile revealed a single site D1-like or D1 receptor in the feline renal cortex with a Kd = 7.8 +/- 1.0 nmol/L and Bmax = 76.5 +/- 19.5 fmol/mg. Competitive binding studies for [3H]-SCH 23390 against unlabeled agonists yielded the following Ki values and rank order of competition: SKF38393 (Ki = 0.47 +/- 0.26 micro m) > fenoldopam (Ki = 3.12 +/- 1.1 micro m) > DA (Ki = 933.1 +/- 1.6 micro m). Competitive binding studies for [3H]-SCH-23390 against unlabeled antagonists yielded the following rank order of competition: SCH 23390 (Ki = 1.97 +/- 0.81 micro m) > spiperone (Ki = 3.79 +/- 0.79) > metoclopramide (Ki = 4.26 +/- 2.4 micro m). Western blot analysis with anti-DA D1 receptor antibodies detected a single band with Mr of 74 kDa corresponding to a D1 DA receptor. These results suggest that a putative D1-like or D1 receptor exists in feline kidneys different from those previously identified in rat, dog or human kidneys.     

Progesterone receptors in feline mammary adenocarcinomas

Estradiol and progesterone receptors were measured in tumor cytosols from 3 intact and 4 neutered female cats with spontaneously occurring mammary adenocarcinomas. Serum from 2 of the intact cats which had been in estrus 4 and 4 to 6 weeks before tumor excision contained progesterone concentrations of 16.2 and 2.2 ng/ml, respectively; serum progesterone in the other cats was less than 2 ng/ml. Estradiol receptors were not detected in any cytosols. Progesterone receptors were detected in all of the cytosols, in concentrations ranging from 4.0 to 11.7 (mean = 7.2) fmol/mg of protein. Scatchard plot analysis of tumor cytosol from an 8th cat with mammary adenocarcinoma revealed presence of high affinity progesterone binding with a dissociation constant (Kd) of 3.47 nM. Tumor receptor content could not be correlated with stage of the estrous cycle nor with whether the cat was intact or neutered.     

琅琊鸡胚MSX2基因克隆及发育性表达变化

【目的】 克隆鸡Msh同源框2(Msh-homeobox 2，MSX2)基因，并对其进行生物信息学和胚胎期表达模式分析，为进一步研究MSX2基因的结构和功能提供支持。【方法】 对80枚琅琊鸡种蛋进行孵化，分别于孵化期第1、2、3、4、5、6、9、12、15、18天采集样品(1~6胚龄采集整胚，9、12、15、18胚龄分别采集心脏和肝脏)，提取总RNA，利用RT-PCR方法扩增并克隆MSX2基因，对其进行生物信息学分析;利用实时荧光定量PCR技术分析MSX2基因在琅琊鸡鸡胚和组织中的表达水平。【结果】 成功克隆了琅琊鸡胚MSX2基因，序列长度为818 bp，开放阅读框为780 bp，编码259个氨基酸。琅琊鸡MSX2氨基酸序列与日本鹌鹑、秃鹰和仓鸮的相似性最高，均为99.23%，与山羊的相似性最低，为74.54%;系统进化树分析结果显示，琅琊鸡与日本鹌鹑聚为一类。生物信息学分析表明，MSX2蛋白分子质量为28 235.18 u，等电点(pI)为9.71，没有信号肽和跨膜域，为不稳定的亲水性蛋白，主要分布在细胞核(60.9%);存在37个磷酸化位点、8个O-糖基化位点和1个N-糖基化位点;二级结构主要由无规则卷曲(63.32%)和α-螺旋(28.19%)组成。实时荧光定量PCR分析表明，MSX2基因在整胚(1~6胚龄)中的表达水平呈现先上升后下降趋势，且在4胚龄时表达水平最高，极显著高于1、2、3胚龄(P<0.01);MSX2基因在12胚龄鸡心脏中的表达水平极显著低于9胚龄(P<0.01);在9~18胚龄鸡肝脏中的表达量呈逐渐下降趋势，且在9胚龄鸡肝脏中表达水平最高(P<0.05)。【结论】 试验成功克隆了琅琊鸡MSX2基因序列，其表达模式在不同胚龄和同一胚龄不同组织间存在差异，为进一步探索琅琊鸡MSX2基因的结构和功能奠定了基础。     

Quantification of naloxone binding sites in brains from suckled beef cows during postpartum anestrus and resumption of estrous cycles

Thirty beef cows, approximately 3 yr of age, were randomly assigned to be slaughtered on d 7, 14, 28, 42 or 56 postpartum. Each cow suckled one calf until slaughter. Data from cows slaughtered on d 42 and 56 were pooled and further classified as anestrous or cyclic based on the presence of a corpus luteum and elevated serum concentrations of progesterone at slaughter. Specific binding of [3H]naloxone (3H-NAL) to homogenates of tissue from hypothalamus (HYP), preoptic area (POA) and basal forebrain (BF) was assessed using multiple-point Scatchard analyses. Nonspecific binding was estimated in the presence of 10(-6) M naloxone. Separation of bound from free 3H-NAL was achieved by centrifugation at 20,000 X g. Concentration (fmol/mg original tissue wet wt) of 3H-NAL binding sites in POA tissue was higher (P less than .05) on d 28 postpartum in anestrous cows than in cyclic cows on d 42 + 56 postpartum (2.58 +/- .32 vs 1.58 +/- .10). When all anestrous cows were compared with cyclic cows, concentrations of 3H-NAL binding sites in POA tissues and in BF tissue were higher (P less than .05) in anestrous cows (anestrous POA, 2.12 +/- .17, cyclic POA, 1.58 +/- .10; anestrous BF, 2.94 +/- .41, cyclic BF, 2.19 +/- .16). Compared across brain regions for all cows, the concentration of specific binding sites for 3H-NAL was greater (P less than .01) in BF (2.5 +/- .2) than in POA (1.9 +/- .1) and greater (P less than .01) in POA than in HYP (1.5 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding characteristics of swine erythrocyte insulin receptors

Crossbred gilts (controls; n = 7) had 8.8 +/- 1.1% (mean +/- SEM) maximum binding of [125I]insulin to insulin receptors on erythrocytes. The number of insulin-binding sites per cell was 137 +/- 19, with a binding affinity ranging from 7.4 X 10(7)M-1 to 11.2 X 10(7)M-1 and mean of 8.8 X 10(7)M-1. Pregnant sows (n = 5) had a significant increase (P less than 0.01) in maximum binding due to an increase in number of receptor sites per cell. Lactating sows fed a high-fiber diet (n = 3) and a low-fiber diet (n = 4) did not develop a significant difference in maximum binding of insulin. Sows fed the low-fiber diet had a significantly higher number of binding sites and a significantly lower binding affinity than did sows fed a high-fiber diet. Receptor-binding affinity was lower in the low-fiber diet group than in cycling gilts, whereas data from sows fed the high-fiber diet did not differ from data for cycling gilts. Data from this study indicated that insulin receptors of swine erythrocytes have binding characteristics similar to those in other species. Pregnancy and diet will alter insulin receptor binding in swine.