Effects of in vivo gonadal hormone environment on in vitro hGRF-40-stimulated GH release

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Abstract
The effects of gender and the gonadal hormone environment on basal and stimulated growth hormone (GH) release by dispersed and continuously perifused rat anterior pituitary cells were examined. Cell from intact male and diestrus day 2 female rats and from castrate male rats either untreated or treated with testosterone (T) or 17.beta.-estradiol (E2) were used. Basal GH release (ng/min per 107 cells; mean .+-. SE) by cells from diestrus day 2 female rats was less than by cells from castrate rats treated with T (4.3 .+-. 0.6 vs. 11.4 .+-. 2.7, respectively; P < 0.025). No other differences in basal release were detected. Concentration-response relationships were documented between human GH-releasing factor 40 (hGRF-40; 0.03-100 nM given as 2.5-min pulses every 27.5 min) and GH release. Mean (.+-.SE) overall GH release (ng/min per 107 cells) above base line was (1) greater by cells from intact male rats (496 .+-. 92) than by cells from castrate (203 .+-. 37.3; P < 0.001), castrate and T-treated (348 .+-. 52.8; P = 0.008), or castrate and E2-treated (58.1 .+-. 6.8; P < 0.001) male rats or by diestrus day 2 rats (68.6 .+-. 9.5; P = 0.0001); (2) greater by cells from castrate and T-treated male rats than by castrate (P = 0.001), castrate and E2-treated (P = 0.0001), or diestrus day 2 (P = 0.0001) rats; (3) greater by cells from castrate rats when compared with cells from castrate and E2-treated male rats (P = 0.001) and diestrus day 2 rats (P = 0.001); and (4) no different by cells from castrate and E2-treated male and diestrus day 2 (P = 0.8) rats. These data (1) confirm gender-dependent differences in hGRF-40-stimulated GH release previously reported in vivo and in vitro and (2) suggest that exposure of the anterior pituitary gland in situ to T or estrogen correlates, respectively, with enhanced or diminished hGRF-40-stimulated GH release in vitro.

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