Gonadotropin-releasing hormone-stimulated luteinizing hormone secretion by perifused pituitary cells from normal, gonadectomized, and testicular feminized rats.

To elucidate further the manner in which gonadal steroids influence the secretion of LH, we examined the effects of gonadectomy and the absence of functional androgen receptors on GnRH-induced LH release from dispersed rat anterior pituitary cells. Intact and gonadectomized (GNX) normal rats and androgen-resistant, testicular feminized (Tfm) animals from the King x Holtzman strain (a mutant strain that possesses defective androgen receptors) were used. Dispersed pituitary cells were perifused with Medium 199 during a 4-h equilibration period and then subjected to eight 2.5-min pulses of GnRH introduced at 30-min intervals at concentrations ranging from 0.03-100 nM. Basal LH secretion by cells from intact male and female rats was indistinguishable (P = 0.79) and was substantially lower (P less than 0.0001) than that by cells from GNX male and female animals. Basal LH secretion by cells from Tfm rats was significantly higher (P less than 0.01) than that by cells from intact animals, but lower (P less than 0.005) than that by cells from GNX animals. In response to GnRH, perifused pituitary cells from animals representing all experimental groups demonstrated concentration-dependent LH release. Pituitary cells from intact female rats showed an overall greater (P less than 0.05) response to GnRH than cells from intact male rats. Pituitary cells from Tfm rats demonstrated a greater GnRH-stimulated LH mean response than cells from intact male (P less than 0.0001) or intact female (P less than 0.0001) rats. Gonadectomy of male rats resulted in an overall GnRH-stimulated LH release similar to that exhibited by cells from gonadectomized female rats (P = 0.61). Cells from Tfm animals released more LH in response to GnRH than those from gonadectomized male and female rats (P less than 0.001). These data demonstrate that the release of LH in response to GnRH by pituitary cells from intact male rats (i.e. in the presence of androgen and functional androgen receptors) is less than that seen by cells from intact females rats. Since circulating levels of testosterone and estradiol are known to be elevated in the testicular feminized rat, the heightened GnRH-stimulated LH release by cells from such animals may reflect either the long term lack of androgenic influence and/or the combined effects of androgen resistance and elevated levels of circulating estrogens.

Growth hormone secretion by individual somatotropes of the testicular feminized rat.

To investigate the cellular mechanisms underlying the unique GH secretory apparatus of the androgen-resistant testicular feminized (Tfm) rat we employed a reverse hemolytic plaque assay to assess GH secretion by individual cells from normal male, normal female, and Tfm rats. Acutely dispersed pituitary cells were incubated for 90 min with GH anti-serum in the presence of medium alone, 0.01, 0.1, 1, 10, or 100 nM GHRH, or 3 microM forskolin after which hemolytic plaques were developed over an additional 30 min. Body weights of the Tfm rats [318 +/- 7 g (mean +/- SEM)] were intermediate between intact males (372 +/- 18 g) and females (218 +/- 7 g). The total number of cells recovered from dispersion of Tfm rat pituitaries [3.20 +/- 0.42 X 10(6) (mean +/- SEM)] was greater than that from males (1.43 +/- 0.12 X 10(6); P = 0.001), but not distinguishable from that from females (2.31 +/- 0.30 X 10(6); P = 0.06). However, the absolute population of recovered somatotropes from the Tfm animals (1.24 +/- 0.22 X 10(6) exceeded both male (0.56 +/- 0.10 X 10(6); P = 0.002) and female (0.80 +/- 0.14 X 10(6); P = 0.046) values. Mean basal and maximal GH plaque areas were greater for cells from male rats than for those from either female or Tfm rats (P less than 0.05) regardless of whether GHRH or forskolin was used as the secretagogue. Plaque areas from female and Tfm cells were indistinguishable under all study conditions. These data suggest that a deficiency of androgen receptors prevents establishment of the greater GH secretory capacity of individual somatotropes characteristic of the adult male rat. This androgen receptor-dependent modulation of GH secretory capacity appears to occur at a step distal to the GHRH receptor. The data also suggest that an increase in the absolute population of somatotropes is an additional consequence of androgen receptor deficiency. This combination of individual somatotropes, each possessing a GH secretory capacity similar to that of cells from normal females, but present in greater absolute numbers, may explain the intermediate values found during previous studies of the Tfm rat GH axis which were based on assessment of large mixed populations of pituitary cells.

Growth hormone (GH) response to GH-releasing hormone by perifused pituitary cells from male, female, and testicular feminized rats.

To determine whether a normal complement of androgen receptors is required to permit full expression of sex-related differences in pituitary GH secretion, we compared the GHRH-stimulated GH secretory responses of continuously perifused anterior pituitary cells from normal male, normal female, and androgen-resistant testicular feminized (Tfm) rats. In each experimental replicate, acutely dispersed pituitary cells were exposed to GHRH (0.03-100 nM) administered as 2.5-min pulses in random order at 30-min intervals. The eluate was collected in 5-min fractions for GH determination by RIA. Basal unstimulated secretion of GH by cells from male rats was greater than that by cells from female (P = 0.007) and Tfm (P = 0.03) rats; basal secretion by the other two groups was similar (P = 0.55). Linear concentration-response relationships between GHRH and GH release were defined for cells from male (P = 0.0002), female (P = 0.0001), and Tfm (P = 0.0002) rats. Overall GHRH-stimulated GH secretion by cells from male rats was greater (P less than 0.0001) than that by cells from female rats. Overall secretion by cells from Tfm rats was less (P less than 0.001) than that by cells from male rats but greater (P less than 0.001) than that by cells from female rats. For all experimental groups, body weight was strongly correlated with both basal (r2 = 0.42; P = 0.001) and GHRH-stimulated (r2 = 0.53; P = 0.0001) GH secretion by the dispersed pituitary cells. These data suggest that a deficiency of androgen receptors results in a diminution of the in vitro GH secretory capability of anterior pituitary cells to a level below that by cells from normal males, but not to the level in normal females. The intermediate position of cells from the Tfm rat may represent a partial masculinization or defeminization within this generally female phenotype.