Chronic effect of TRH and LRH upon a series of basophils along with the serum and pituitary TSH, LH and FSH concentration.

Abstract

Chronic s.c. injections with synthetic TRH [thyrotropin-releasing hormone] (10 .mu.g/0.2 ml of gelatin-saline) for 21 days slightly raised not only [rat] serum TSH [thyrotropine] but also serum LH [luteinizing hormone] concentration; those for 7 days tended to diminish the serum LH and FSH [follicle stimulating hormone] concentration. The magnitude of rise in the serum TSH was approximately equivalent to 1/5 of the value 30 days after a single injection with the same dose of TRH. Injections of synthetic LRH (5 .mu.g/0.2 ml) for 21 days raised serum LH concentration 3.5 times as high as a single injection did. Pituitary TSH concentration was lowered conspicuously after TRH injections for 21 days; pituitary LH concentration was diminished remarkably after LRH injections for 21 days. Serum FSH concentration was not changed by the same LRH injection, while pituitary FSH concentration was diminished. Injections of TRH and LRH in combination for 7 or 21 days lowered the pituitary LH and FSH content more extensively than the separate LRH injection for 7 or 21 days. A possible synergistic or countervailing influences of the releasing hormones upon the secretion of the other trophic hormones was suggested. This is contradictory to the concept that one releasing hormone is responsible for 1 target cell. This discrepancy may be explained by a working hypothesis as to the secretory cycle of the basophil. Each releasing hormone apparently did not act limitedly upon 1 target cell but universally upon a series of basophils. Both TRH and LRH exerted analogous morphokinetic functions to convert the II-type cell (classical thyrotroph) into the III-type cells (classical LH-gonadotrophs) which are destined to turn into the III/IV- and IV-type cells (classical FSH-gonadotrophs), and to revert them to the original II-type cells in the course of secretory cycle. The releasing hormone might accelerate the rotation of secretory cycle of the basophil. The various types of basophils may not be independent of each other, but may modify their shape and property according to the different phases of secretory cycle, i.e., synthesizing, storing, secreting and resting phases. The II/III- and III-type cells were particularly accumulated after a long-term TRH injection; the IV/II- or II-type cells were accumulated but the IV-type cells were diminished in number after a separate LRH injection or the TRH and LRH injections in combination. The accumulation of the resting cells (IV/II-type) may account for the temporal stabilization of secretory cycle by the chronic injection.