野生鲇鱼生长激素分泌的季节变化及其神经内分泌调控

SEASONAL CHANGES AND NEUROENDOCRINE REGULATION OF GROWTH HORMONE SECRETION IN FERAL CATFISH (SILURUS ASOTUS)

采用离体垂体碎片灌流孵育系统 ,将处于性腺退化期野生鲇鱼垂体切成约 1mm3 的碎片 ,用M 199冲洗之后放入灌流柱的两层Cytodex -Ⅲ微载体之间 (温度为 19± 1℃ )。每 5分钟收集一管灌流液 ,- 2 5℃贮存待测GH。采用鲤鱼GH放射免疫测定方法 (cGHRIA)测定鲇鱼垂体碎片灌流液以及血清和垂体中的GH含量。结果表明 :促黄体素释放激素类似物 [desGly10 (D Ala6)LHRHethylamide ,LHRH A]不能显著刺激离体垂体碎片基础GH分泌 ,注射LHRH A后不能显著提高血清基础GH水平 ;注射DA能显著提高鲇鱼血清基础GH水平 ,APO能以剂量依赖方式显著刺激垂体碎片基础GH分泌。雌、雄鲇鱼血清GH水平在 6月达到峰值 ,垂体GH水平在 3月和 7月份各出现一个峰值 ,各个季节雌鱼垂体和血清GH水平均显著高于雄鱼。鲇鱼血清和垂体GH水平与生殖周期有密切联系。

The catfish ( Silurus asotus ) distributes widely throughout the freshwaters of China, Korea and Japan, and is a high commercially valuable aquaculture fish in the north region of China. The natural stocks of this species have decreased gradually in recent years, therefore, it is desirable to study endocrine physiology of the feral catfish, particularly seasonal changes of growth hormone (GH) secretion and their regulation control mechanism. To date, there have been no published study on GH secretion and regulation in this catfish. In the present study, we investigated seasonal changes in the serum and pituitary gland GH levels and the response to neurohormone and dopaminergic drugs \%in vitro\% and in vivo stimulation of GH release. In vitro experiment were conducted using a validated pituitary fragments perifusion system. Briefly, the pituitary glands collected from sexually regressed female feral catfish from Pearl River, were chopped into fragments (1 mm 3) and were washed with medium 199 and placed between two layers of Cytodex Ⅲ beads in the perifusion columns at 19±1℃. In each experiment, two pituitary glands were each divided into two identical parts, and transferred to four perifusion chambers and perifused immediately. Five minute fractions of perifusate were collected with a LKB fraction collector and stored at -25℃ for growth hormone (GH) assay. GH levels in perifusate, serum and pituitary gland were measured by using a validated GH radioimmunoassay (RIA) for common carp. Luteinizing hormone releasing hormone analogs [des Gly 10 (D Ala 6)LHRH ethylamide,LHRH A] were prepared as a stock solution of 10 -5 M in 0 8% NaCl and stored at -25℃,and was diluted in perifusion medium to the working concentrations just before use. Apomorphine (APO), a agonist of dopamine (DA), was dissolved in 0 8% NaCl, and diluted in perifusion medium to the working concentration prior to use. Perifusion of two minute pulses of different concentrations of LHRH A (101 001 000 nmol/L) failed to stimulate GH release by in vitro pituitary fragments, and the injection of LHRH A ( 0 01 μg /g.b.w.) was ineffective to enhance GH levels in the serum. Injection of DA (50 μg/g.b.w.) potentiated significantly ( P <0 05) GH levels in the serum. Perifusion of two minute pulses of different concentrations of APO (101 001 000 nmol/L) increased significantly ( P <0 05) GH release of the pituitary fragments in a dose dependent manner. Female and male catfishes were serially blood sampled in March, April, June, July, September, and December by puncturing the caudal vasculature with a 25 guage 1 3 cm needle attached to a 1 2 ml disposable syringe. Blood samples were allowed to clot on ice for several hours, and the serum separated by centrifugation and stored at -25℃.After dissecting the skull, pituitary was removed and stored at -25℃for measurement of GH contents. The serum and pituitary GH levels were determined by GH RIA. Results indicated that there was one basal GH peak in the serum in June, and there were two basal GH peaks in the pituitary in March and July respectively. Seasonal basal GH levels in the serum and pituitary gland of female catfishes were significantly higher than those of male catfishes. These results suggest that seasonal changes of basal GH levels in the serum and pituitary gland are evidently correlated to the reproductive cycle.