LH and estradiol concentration in the blood and morphological characteristics of the hypothalamus, hypophysis and the ovaries of sheep after LH/FSH-RH and synthetic gestagen treatment.

In the experiments the effect of synthetic LH/FSH-RH on the concentration of LH and estradiol 17-beta (E2) in the blood of sheep was followed during physiological anestrus, and the preovulatory LH release and the E2 level in the blood serum after the synchronization of estrus with chlormadinone acetate (CAP) were studied. Furthermore, the nuclear volumes of the neurons in the ncl. hypothalamicus anterior (NHA), ncl. paraventricularis (NPV), ncl. arcuatus (NARC) and the pars distalis ncl. mamillaris medialis (PD NMM) as well as the percentage numbers of the adenohypophyseal cells and the number of normal and atretic tertiary follicles of the same ewes are described. The results show that after synthetic LH/FSH-RH treatment the LH concentration gradually increases in the blood, intravaginally instilled CAP affects the hypothalamic neurons probably by increasing significantly the concentration of the endogenous E2 that sensitizes the receptors of the hypothalamo-hypophyseal structures to LH/FSH-RH, enhancing, thus, its effect. The changes in the nuclear volume of the neurosecretorial cells of the hypothalamus after the administration of the mentioned substances indicate an ultrashort feed back in the regulation of secretion and the LH/FSH-RH release by the NARC cells. The changes were considered from the viewpoint of influencing the estrous cycle and the productivity of ewes.