EFFECTS OF PROGESTERONE AND CORTISOL ON THE RELEASE OF GONADOTROPIN-RELEASING-HORMONE FROM THE PERIFUSED PITUITARY STALK-MEDIAN EMINENCE AND ON LUTEINIZING-HORMONE RELEASE FROM THE PITUITARY OF COWS
N. Kawate et al., EFFECTS OF PROGESTERONE AND CORTISOL ON THE RELEASE OF GONADOTROPIN-RELEASING-HORMONE FROM THE PERIFUSED PITUITARY STALK-MEDIAN EMINENCE AND ON LUTEINIZING-HORMONE RELEASE FROM THE PITUITARY OF COWS, Animal reproduction science, 34(2), 1993, pp. 93-100
The direct effects of progesterone and cortisol on the release of gona
dotropin-releasing hormone (GnRH) and luteinizing hormone (LH) were ex
amined by perifusing tissues from the bovine pituitary stalk-median em
inence and the anterior pituitary. These tissues were isolated and per
ifused for 160 min and 8 h, respectively. To assess the effect of prog
esterone and cortisol, from 0 to 10 mu M of progesterone or cortisol w
as added separately to the tissues and the amounts of GnRH and LH assa
yed in the effluent medium. The release of GnRH from the hypothalamic
fragments was significantly reduced within 20 min after the addition o
f 0.1 and 10 mu M of progesterone when compared with the values for th
e control group (P<0.05), but GnRH release was not markedly affected b
y the addition of up to 10 mu M cortisol. Spontaneous release of LH fr
om the anterior pituitary was not markedly affected by the addition of
0.1 or 10 mu M progesterone, although the GnRH-stimulated release of
LH was significantly higher than that of the control group (P<0.05). G
nRH-stimulated release of LH was not markedly affected by addition of
cortisol. These results suggest that high concentrations of progestero
ne act directly on the bovine pituitary stalk-median eminence to inhib
it the release of GnRH, but they enhanced the release of LH from the a
nterior pituitary in response to the same GnRH stimulus.