Effect of low salinity on the expression profile of Na+/K+‐ATPase and the growth of juvenile chub mackerel (Scomber japonicus Houttuyn)

Chub mackerel (Scomber japonicus Houttuyn) is one of the most commercially important scombroid fish used as a food resource. Recently, there has been a demand for efficient rearing methods of this fish for a full‐life cycle aquaculture. In the present study, we evaluated the physiological responses in the juvenile S. japonicus to different ambient salinities. A significantly higher gain of the body mass was observed in the juveniles reared in 24 g/L and 13 g/L seawater than in those reared in natural seawater (34 g/L) within 40 days of the experimental period without affecting mortality. A principal enzyme for osmoregulation, Na⁺/K⁺‐ATPase, was expressed in the ionocytes located in the gill filaments of the juveniles. The number and the cell size of ionocytes and the enzymatic activity of Na⁺/K⁺‐ATPase in the gills decreased within 10 days after the low‐salinity challenge, which implies the reduction of the energy‐consuming active ion secretion under the low‐salinity environment. The physiological capacity for adaptation to low‐salinity seawater in chub mackerel could be basic knowledge to carry out culturing of these fish in coastal sea pens where ambient salinity fluctuates. The improvement of the growth performance by rearing in low‐salinity seawater will contribute to the efficient production of the seed juveniles for aquaculture.     

Body growth and plasma concentrations of metabolites and metabolic hormones during the pubertal period in female Shiba goats

It has been shown in various species that the onset of puberty is closely associated with body growth and nutritional state rather than age. The present study was conducted to determine the timing of puberty and to clarify body growth and metabolic changes around the pubertal period in female Shiba goats. Blood samples were collected between 10 to 38 weeks of age from 12 female goats, and plasma concentrations of progesterone, metabolites (glucose, nonesterified fatty acid, ketone body and acetic acid) and metabolic hormones (insulin and insulin-like growth factor-I (IGF-I)) were analyzed. Physical parameters (body weight, withers height and body length) were also measured at the blood sampling. The week when plasma progesterone concentrations first exceeded 1.0 ng/ml was designated as the onset of puberty. The results showed that the average age of the onset of puberty was 27.0 +/- 0.9 (mean +/- SEM) weeks in female Shiba goats. When the goats reached puberty, the average values of body weight and goat body mass index ((body weight (kg)/withers height (cm)/body length (cm)) x 10(3)) were 12.2 +/- 0.5 kg and 5.7 +/- 0.2, respectively. No particular change associated with puberty was apparent for plasma concentrations of the metabolites examined. Plasma insulin concentrations were maintained at lower levels until the onset of puberty, and then they began to gradually increase. Plasma IGF-I concentrations began to gradually increase 1 to 4 weeks before the onset of puberty and this increase continued throughout the peripubertal period. These results imply that IGF-I acts as a peripheral nutritional signal to trigger the onset of puberty in Shiba goats.     

Acute lipoprivation suppresses pulsatile luteinizing hormone secretion without affecting food intake in female rats

The present study examined the effect of acute lipoprivation on pulsatile luteinizing hormone (LH) secretion in both normal-fat diet, ad libitum-fed and fasted female rats. To produce an acute lipoprivic condition, mercaptoacetate (MA), an inhibitor of fatty acid oxidation, was administered intraperitoneally to ad libitum-fed or 24-h fasted ovariectomized (OVX) rats with or without an estradiol (E2) implant, that produces a negative feedback effect on LH pulses. The steroid treatment was performed to determine the effect of estrogen on lipoprivic changes in LH release, because estrogen enhances fasting- or glucoprivation-induced suppression of LH pulses. Pulsatile LH secretion was suppressed by MA administration in a dose-dependent manner in the ad libitum-fed OVX and OVX+E2 rats. LH pulses were more severely suppressed in the 24-h-fasted OVX and OVX+E2 rats compared to the ad libitum-fed rats. Estrogen slightly enhanced lipoprivic suppression but the effect was not significant. In the present study, increased plasma glucose and free-fatty acid concentrations may indicate a blockade of fatty acid metabolism by the MA treatment, but food intake was not affected by any of the MA doses. Acute vagotomy did not block lipoprivic suppression of LH pulses. Thus, the present study indicates that lipid metabolism is important for maintenance of normal reproductive function even in rats fed a normal-fat diet and lipoprivation may be more critical in fasted animals that probably rely more heavily on fatty acid oxidation to maintain appropriate metabolic fuel levels. In addition, failure of blockade of lipoprivic LH inhibition by vagotomy suggests that lipoprivic information resulting in LH suppression is not transmitted to the brain via the vagus nerve.     

Collateral uterine blood flow in Holstein cows during the third trimester of pregnancy

Blood flow to the gravid and nongravid uterine horns of four multiparous Holstein cows (mean +/- SD, BW=641.8 +/- 95.4 kg; age=4.8 +/- 1.2 years; parity=3.0 +/- 1.2) was measured on days 225, 248, and 266 of gestation. Surgery was conducted on day 214.5 +/- 4.0 of gestation through the flank of the standing cows. Transit-time ultrasonic flow probes (diameter 12 or 14 mm) were fitted surgically around the uterine arteries of each cow. Surgery was completed within two hours of anesthesia, and the animals recovered rapidly following surgery. Uterine blood flow (UBF, l/min) was recorded at 10 sec intervals for approximately 23.5 hours; these values were averaged to determine UBF. The mean gravid UBF was significantly (P<0.05) greater than the nongravid UBF in this study. The range of the gravid and nongravid UBFs varied from 3.61 to 14.05 and 0.72 to 6.54 l/min, respectively. There were no changes (P>0.1) in the mean gravid and nongravid UBFs from day 225 to 266 of gestation.     

Time course of final oocyte maturation and ovulation in chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> induced by hCG and GnRHa

Abstract:   The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two 'opposite' times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.     

Gonadotropins, gonadotropin receptors and their expressions during sexual maturation in yellowtail, a carangid fish

To study the physiological roles of gonadotropins (GtHs) in the yellowtail, the cDNAs encoding each GtH subunit (GPHα, FSHβ and LHβ) and their receptors (FSHR and LHR) were isolated from the pituitary gland and gonads using the polymerase chain reaction (PCR). In addition, thyrotropin (TSH) and its receptor (TSHR) cDNAs, were isolated from the pituitary gland, ovary and testis. The changes in the mRNA levels of each subunit were determined at different stages of maturation. The isolated cDNAs of GPHα, FSHβ, LHβ and TSHβ were 662, 545, 595 and 879 bp long, respectively. The amino acid sequence identity of the yellowtail GPHα, FSHβ, LHβ and TSHβ subunits was 85–63, 68–33, 93–65 and 74–46%, respectively, as compared with other fish species. Northern blot analysis showed that GPHα and FSHβ were strongly expressed in pituitary at the early vitellogenic stage and during spermatogenesis, whereas LHβ was expressed significantly in the late vitellogenic stage, and in both spermatogenesis and spermiation. Full-length cDNAs encoding FSHR, LHR, and TSHR were obtained from the testes and ovaries. The FSHR, LHR and TSHR cDNA encoded a protein of 680, 702 and 778 amino acids, and showed the highest identity with tilapia FSHR (76%), tilapia LHR (84%) and striped bass TSHR (94%), respectively. Northern blot analyses indicated that all of these receptors are expressed differently at different stages in the ovaries and testes.     

Seasonal characteristics of surface water quality in the wastewater catchment system of an urbanizing basin

Vientiane, Lao PDR, has been subject to extensive and ongoing urbanization plans, including development of natural marshes and residentialization of paddy fields into suburban areas, despite natural marshes playing a vital role in treating wastewater from urban areas. Therefore, it is important to understand the current situation regarding the nutrient balance in these natural wastewater treatment systems to predict future conditions and design appropriate measures against water quality deterioration. However, limited data are available in Vientiane on the hydrological characteristics of water and nutrient runoff that flow into marshes through drainage canals. In this study, we conducted a periodic survey of drainage canals and Mak Hiao River in the wastewater catchment system surrounding Vientiane during the rainy and dry seasons. We monitored the discharge of surface water at 21 observation sites and analyzed water quality of nitrogen, phosphorus, and total organic carbon. These observations revealed that the concentrations of dissolved nitrogen and phosphorus were significantly higher at sites in urban areas, followed by sites in the main river basin and those in agricultural areas. Dissolved nitrogen and phosphorus concentrations varied with runoff discharge, especially in urban and river basin sites, with lower concentrations in the rainy season and higher concentrations in the dry season. On the other hand, we found no significant differences between the rainy and dry seasons in nutrient concentrations in the agricultural basin. Finally, we proposed measures to counteract the deterioration of water quality during dry seasons and simulated the impact of these measures.     

Lignans ofChamaecyparis obtusa

Heartwood ofChamaecyparis obtusa contains significant amounts of a dibenzylbutyrolactone lignan, hinokinin (8). This investigation demonstrated that the contents of 8 and a norlignan, hinokiresinol (12), were higher in the heartwood region than in the sapwood, indicating their nature of being heartwood extractives. Eleven lignans — xanthoxylol (1), 7-oxohinokinin (2), savinin (3), dihydrosesamin (4), isoactifolin (5), sesamin (6), piperitol (7), hinokinin (8), pluviatolide (9), haplomyrfolin (10), and rnatairesinol (11) — were isolated from young shoots ofChamaecyparis obtusa cv. Breviramea. Eight lignans (1, 2, 4, 5, 7, 9,10, and11) were isolated from this plant for the first time. Chiral high-performance liquid Chromatographie analysis showed that8, 9, 10, and11, were found to be levorotatory and optically pure (>99% e.e.). Based on the chemical structures of the isolated lignans, possible biosynthetic pathways of8 are discussed.Parts of this report were presented at the 44th annual meeting of the Japan Wood Research Society, Nara, April 1994; the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996; and the 44th Lignin Symposium, Gifu, October 1999