A. P. S. Dhariwal

Failure of Inhibitors of Protein Synthesis to Affect the LH-Releasing Action of Hypothalamic Extracts in Vitro∗

Summary Anterior pituitary halves from adult male rats were incubated in vitro for 6 hours following a preincubation of 30 min in tissue culture medium 199. The LH release from the glands was determined by the ovarian ascorbic acid depletion assay. Neither puromycin nor actinomycin in doses of 10-80 μg/ml interfered with the “basal” release of LH from the pituitaries. Purified LH-releasing factor (LHRF) enhanced the release of LH, and this enhancement was not influenced by the presence of either of the antibiotics. The LHRF can thus act when protein synthesis is blocked and must facilitate release of preformed LH from the cell. The present results with LHRF are different from those previously obtained with FSHRF whose action in increasing FSH release was blocked by the antibiotics and therefore appeared to require protein synthesis.

Regulation of Gonadotrophin and Prolactin Secretion by Hypothalamic Neurohumoral Factors

The secretion of gonadotrophins and prolactin by the adenohypo-physis is influenced by a variety of environmental and hormonal factors. There are many examples of neurally mediated environmental influences. Exposure of rats to constant lighting results in the development of constant vaginal oestrus associated with a blockade of cyclic ovulation. Lactation, presumably operating via the stimulus of nursing, augments prolactin release and inhibits secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) (McCann and Ramirez, 1964; Everett, 1964).

The Physiology and Biochemistry of Luteinizing Hormone-Releasing Factor and Follicle Stimulating Hormone-Releasing Factor

Hypothalamic control over the secretion of the anterior pituitary gland has become almost universally accepted and attention has shifted to attempts to clarify the mechanism by which the hypothalamus influences the gland. A great deal of indirect evidence has supported the concept that this control is exerted by a neurohumoral pathway via the hypophysial portal vessels. The following discussion will summarize the evidence obtained in our laboratory for the existence, physiological significance, chemical nature, and mode of action of two neurohumoral agents which appear to regulate the output of gonadotrophins. The first of these to be discovered was a luteinizing hormone-releasing factor (LRF), the second a follicle stimulating hormone-releasing factor (FRF). Each of these substances appears to regulate the output of the respective pituitary trophic hormone.

Effects of Chronic Administration of Sheep Stalk-Median Eminence Extract on Organ Weights of Immature Hypophysectomized Rats with Pituitary Grafts

Summary Single pituitary grafts from donors of the same sex maintained some growth and led to slight maintenance of testes in male and uteri in female hypophysectomized rats. There was slight maintenance of adrenal weight in both sexes. Injection of crude sheep stalk-median eminence (SME) extracts resulted in a further significant increase in testes and ventral prostate weights in hypophysectomized, grafted males and in uterine and ovarian weights in grafted females on comparison to the weights of these organs in grafted animals injected with cerebral cortical extract. Adrenal weight was increased in rats of both sexes by SME extract. The results provide evidence that chronic injection of hypothalamic extract can increase the weight of pituitary target organs in both male and female rats presumably via stimulation of both release and synthesis of pituitary hormones.