Regulation of prolactin secretion by hypothalamus in some cold blooded vertebrates

Effect of homoplastic hypothalamic extract (HHE) on the release of prolactin from the pituitary gland of three aquatic animals -- the fish, Clarias batrachus, the amphibian, Rana tigrina and the reptile, Natrix piscator was studied. Release of prolactin from the pituitary gland in the above animals was blocked within 4 hours by CG 603 (100 microgram/g body wt.) injection. Administration of HHE and perphenazine (15 microgram/g body wt.) in such animals resulted in significantly increased level of prolactin in the blood serum within one hour of treatment indicating an accelerated release of prolactin from the pituitary gland. Injection of cerebral cortical extract failed to induce such response in any of the specimens. From the findings of the present experimentation it is evident that the hypothalamus in C. batrachus, R. tigrina and N. piscator contained predominantly prolactin-release stimulatory factor (PRF) at the time of assessment. Probably in the aquatic poikilotherms where prolactin is not essential for their survival in hypophysectomized condition, hypothalamus contains PRF at least for some period in a year.