Persistence of immunoreactive TRH and GnRH in long-term primary anterior pituitary cultures

Intact anterior pituitary tissue and primary anterior pituitary cultures were stained with 1:30,000 anti-TRH and 1:10,000 anti-GnRH using the peroxidase antiperoxidase immunocytochemical technique. Stains applied to serial ultrathin sections of intact pituitaries showed that TRH immunoreactivity could be localized in secretory granules of thyrotropes, gonadotropes and corticotropes whereas GnRH immunoreactivity was found only in gonadotropes and corticotropes. Long-term primary pituitary cultures were studied to remove the anterior pituitary cells from hypothalamic influences. In these cell populations both TRH and GnRH immunoreactivity persisted. In addition, quantification of the stained cells at the light microscopic level demonstrated that the volume fraction of TRH and GnRH immunoreactive cells remained constant up to 3 weeks of culture. Studies of serial ultrathin sections through cells from these cultures showed TRH or GnRH localized in secretory granules of cells that contained LH and ACTH, but not TSH. Both liquid and solid phase immunoabsorption specificity controls were used to validate the immunocytochemical stains. These studies suggest that the pituitary TRH and GnRH immunoreactivities may not be completely of hypothalamic origin, but may also be endogenous to a subpopulation of unique multihormonal pituitary cells.     

Detection of luteinizing hormone beta messenger ribonucleic acid (RNA) in individual gonadotropes after castration: use of a new in situ hybridization method with a photobiotinylated complementary RNA probe

Patterns of gonadotropin storage in individual gonadotropes change with alterations in the physiological state. After castration in the male rat, there is a 2.5-fold increase in the percentage of gonadotropes and an increase in the proportion of gonadotropes storing both LH and FSH. In addition, there are 6- to 8-fold increases in the pituitary concentrations of LH beta subunit mRNAs. In order to determine whether these changes are due to increases in the number of gonadotropes containing subunit mRNA, or the amount of mRNA per cell or both, an in situ hybridization technique using a photobiotinylated rat LH beta cRNA probe (bio-LH beta-cRNA) was applied to detect LH beta mRNA in fixed whole rat pituitary cells from intact or castrated rats. After hybridization, the bio-LH beta-cRNA was localized with either avidin-biotin peroxidase complex or the fluorescent streptavidin phycoprobe methods. The cells containing LH beta mRNA were then counted and the amount of mRNA per cell was measured by video microdensitometry. Ten percent of the anterior pituitary cells from intact animals contained LH beta mRNA. After castration (2-4 weeks) this percentage rose to 19-24.5%. Image and microdensitometric analyses showed that castration produced a 1.9-fold increase in the amount of LH beta mRNA per cell, and a 2.2-fold increase in the area of cells containing LH beta mRNA. Hence, castration resulted in an increase in the level of LH beta mRNA per cell as well as the number of LH beta mRNA-containing cells. When in situ hybridization was followed by immunocytochemistry in cells from intact rats, 83% of gonadotropes that stained for LH beta and 80% of gonadotropes that stained for FSH beta contained LH beta mRNA whereas after castration 99% of LH-storing and 93% of FSH-storing cells contained LH beta mRNA. This new in situ hybridization protocol is rapid and allows quantification of mRNA within individual gonadotropes. In addition, since the hybridization protocol does not apparently alter the gonadotropin antigens, the hormone content of the same gonadotrope may be defined by immunocytochemistry.     

Notch signaling regulates endocrine cell specification in the zebrafish anterior pituitary

The vertebrate pituitary gland is a key endocrine control organ that contains six distinct hormone secreting cell types. In this study, we analyzed the role of direct cell-to-cell Delta-Notch signaling in zebrafish anterior pituitary cell type specification. We demonstrate that initial formation of the anterior pituitary placode is independent of Notch signaling. Later however, loss of Notch signaling in mind bomb (mib) mutant embryos or by DAPT treatment leads to increased numbers of lactotropes and loss of corticotropes in the anterior pars distalis (APD), increased number of thyrotropes and loss of somatotrope cell types in the posterior pars distalis (PPD), and fewer melanotropes in the posterior region of the adenohypophysis, the pars intermedia (PI). Conversely, Notch gain of function leads to the opposite result, loss of lactotrope and thyrotrope cell specification, and an increased number of corticotropes, melanotropes, and gonadotropes in the pituitary. Our results suggest that Notch acts on placodal cells, presumably as a permissive signal, to regulate progenitor cell specification to hormone secreting cell types. We propose that Notch mediated lateral inhibition regulates the relative numbers of specified hormone cell types in the three pituitary subdomains.     

Localization of fertility factor SP22 to specific cell types within the anterior pituitary gland

Sperm protein 22 (SP22) was recently identified in the anterior pituitary gland (AP) of male Golden Syrian hamsters using ion trap mass spectrometry. SP22 has been implicated in apoptosis, androgen receptor function, fertility, and ontogeny of early-onset Parkinson's disease. However, the role of SP22 in the pituitary has not been investigated. We cloned the cDNA for full-length SP22 from AP and posterior lobe (posterior pituitary and intermediate lobe) of the pituitary gland in adult male rats and Golden Syrian hamsters, confirming the presence of SP22 mRNA in the AP and posterior lobe. Because gonadal steroids are important regulators of AP function, and SP22 is associated with androgen receptor function, we used Western blots to compare SP22 in the AP of intact and orchidectomized male rats given placebo or a low or high dose of testosterone. SP22 did not differ with treatment, indicating that AP SP22 concentration was not regulated by testosterone. To localize SP22 to specific cells of the AP, mirror-image paraffin sections were labeled against SP22 and either luteinizing hormone (LH)beta, thyroid-stimulating hormone (TSH)beta, prolactin, adrenocorticotropic hormone (ACTH), or growth hormone (GH) using peroxidase-conjugated secondary antibody. Additional sections were colabeled with SP22 and one of the AP hormones using fluorescent secondary antibodies. SP22 colocalized in somatotropes and thyrotropes in rat and hamster. We identified SP22 in a small percentage of corticotropes, gonadotropes, and lactotropes. This is the first report that SP22 mRNA is present specifically in the AP, and SP22 is localized primarily in somatotropes and thyrotropes. SP22 may help regulate AP function and be particularly important for the control of GH and TSH secretion.     

Cell-specific distributions of estrogen receptor alpha (ERα) and androgen receptor (AR) in anterior pituitary glands from adult cockerels as revealed by immunohistochemistry

Estrogens and androgens play important roles in regulating the hormone-secreting functions of the pituitary gland by binding to their corresponding receptors. However, the expression of estrogen receptors (ERs) and the androgen receptor (AR) and the cell types containing ERs and AR in the anterior pituitary gland of adult chickens have not been well-studied. In this study, the distribution of ERα, AR and their corresponding cell types in the anterior pituitary gland of adult cockerels was detected by immunohistochemistry. The results showed that ERα was expressed in 68.63 % of luteinizing hormone (LH) producing cells but was not found in thyrotropes, lactotropes, somatotropes, corticotropes and folliculo-stellate (FS) cells. Pituitary hormone and AR double labeling results showed that about 37 % of LH cells and 50 % of thyroid-stimulating hormone (TSH) producing cells expressed AR, respectively. In contrast, less than 1 % of the somatotropes had an AR positive signal and AR signals were not detected in lactotropes, corticotropes or FS cells. In addition, there were only a few AR and ERα dual-labeled cells observed. These novel results provide evidence for a cell-specific distribution of ERα and AR in the anterior pituitary from adult cockerels by immunohistochemistry. The different distributions of ERα and AR in the LH cells suggest that the feedback-regulating mechanisms of estrogen and androgen on the pituitary hormones secretion are different. The functions and related mechanisms still need to be elucidated further.     

Targeted ablation of pituitary gonadotropes in transgenic mice.

LH, FSH, and TSH are heterodimeric glycoprotein hormones composed of a common alpha-subunit and unique beta-subunits. The alpha-subunit is produced in two distinct specialized cell types of the pituitary gland: gonadotropes, which synthesize LH and FSH, and thyrotropes, which synthesize TSH. We have demonstrated that 313 base pairs of the bovine-alpha subunit promoter direct expression of diphtheria toxin A chain specifically to the gonadotropes in transgenic mice. Animals carrying this transgene generally exhibit reproductive failure and lack of gonadal differentiation, consistent with gonadotrope ablation. Lack of gonadotrope activity was verified by RIA and immunohistochemical staining for LH. The phenotype of these transgenic mice is nearly identical to mice homozygous for the spontaneous mutation, hpg, which is due to a deletion in the gene encoding GnRH. Thyrotrope function was judged normal based on overall growth of the animals, appearance of their thyroids, T4 levels measured by RIA, and immunohistochemical staining for TSH. The ablation of gonadotropes but not thyrotropes suggests that separate cis-acting elements are necessary for expression of the alpha-subunit gene in these two cell types. Pituitary content of ACTH and GH was apparently normal, while PRL synthesis and storage were reduced. Thus, in a pituitary almost completely devoid of gonadotropes, most other pituitary functions were normal. This suggests that most pituitary cells are able to differentiate independently of terminal gonadotrope differentiation and can function in the absence of paracrine signaling provided by gonadotropes.     

Ultrastructural study of the adenohypophysis of the Chinese hamster.

The adenohypophysis of normal Chinese hamsters of both sexes was examined ultrastructurally. Organs were fixed by intravascular perfusion with S-collidine-buffered glutaraldehyde solution. Seven types of cells were differentiated and, according to morphological characteristics, classified as (1) mammotropes, with very large (400-800 nm) polymorphous secretory granules; (2) somatotropes, either in the storage phase with numerous large, dense granules (average 300 nm), or in the hormone synthesis phase, with abundant endoplasmic reticulum and large Golgi apparatus; (3) corticotropes, with irregular cell shape, and granules (average 160 nm) arranged in lines parallel to the cell membrane; (4) FSH gonadotropes, with abundant and dilated endoplasmic reticulum, and granules (190-320 nm) uniformly distributed in the cytoplasm; (5) LH gonadotropes, with granules (120-220 nm) of varied density; (6) thyrotropes, with irregular cell shape and very small granules (120-160 nm), and (7) agranulated cells. The ultrastructure of the adenohypophysis of the Chinese hamster corresponds closely with observations reported in rats, mice and Syrian hamsters.     

Angiotensin II in the brain and pituitary: contrasting roles in the regulation of adenohypophyseal secretion

Angiotensin II (AII) is present in gonadotropes in rats, and there are AII receptors on lactotropes and corticotropes. AII may be a paracrine mediator that stimulates the secretion of prolactin and adrenocorticotropin (ACTH) at the level of the pituitary, but additional research is needed to define its exact role. Angiotensinogen may also reach the gonadotropes via a paracrine route. On the other hand, there is considerable evidence that brain AII stimulates the secretion of luteinizing hormone (LH) by increasing the secretion of LH-releasing hormone, and that this effect is due to AII-mediated release of norepinephrine from noradrenergic nerve terminals in the preoptic region of the hypothalamus. In addition, brain AII inhibits the secretion of prolactin, probably by increasing the release of dopamine into the portal hypophyseal vessels. Circulating AII stimulates the secretion of a third anterior pituitary hormone, ACTH, by acting on one or more of the circumventricular organs to increase the secretion of corticotropin-releasing hormone.     

Estrogen uptake capacity of individual pituitary cell types from male and female rats one, fourteen and fifty days after castration

A quantitative autoradiographic technique was combined with immunocytochemical staining to compare 3H-estrogen uptake in individual pituitary cell types 1, 14 or 50 days after castration in both male and female rats. Silver grains were counted over nuclei of immunocytochemically stained cells and means were computed for each cell type. The order of labelling intensity for all groups was gonadotropes greater than or equal to lactotropes = somatotropes greater than thyrotropes = corticotropes. In male rats 3H-estrogen uptake capacity in all of these cell types remained unchanged over the post-castration interval. Only gonadotropes from female rats demonstrated a significant change in estrogen uptake capacity over the intervals examined. Uptake in these cells increased by 137% between 1 and 50 days after ovariectomy. At both 14 and 50 days post-ovariectomy, gonadotropes concentrated significantly more radioactive label than either lactotropes or somatotropes. One day after castration, gonadotropes from females concentrated less 3H-estrogen than males while at 50 days after castration they concentrated significantly more than gonadotropes from male rats.     

Gonadotrope and thyrotrope development in the human and mouse anterior pituitary gland

Genes and orthologous intrinsic and extrinsic factors critical for embryonic pituitary gonadotrope and thyrotrope cell differentiation have been identified mainly in rodents, but data on the human are very limited. In human fetal pituitaries examined between 14 and 19 weeks of gestation using immunofluorescent confocal microscopy, we found that most fetal gonadotropes expressed alpha-GSU, LHbeta, and FSHbeta gonadotropin subunits while almost no cells expressed alpha-GSU and LHbeta alone. Gonadotropes expressing alpha-GSU and FSHbeta only were detected in both male and female pituitaries, increasing in proportion to total gonadotropes in both males and females from 14 (approximately 4.5%) to 19 weeks (approximately 16.5%) with a peak in males of 45.5% compared with females of 16.5% at 17 weeks of gestation. When FSHbeta or LHbeta genes were expressed, gonadotropes were non-dividing. This profile of human fetal gonadotrope development differs from the current mouse model. Furthermore, while expression of alpha-GSU appears to be the lead protein in gonadotropes, in thyrotropes which ultimately express alpha-GSU with TSHbeta, we observed that most if not all thyrotropes were TSHbeta-positive but alpha-GSU-negative until around 19 weeks in human, and e15 in mouse, fetal pituitaries. Furthermore, the TSHbeta-only thyrotropes were dividing, and TSHbeta rather than alpha-GSU was the lead protein in thyrotrope development. Thus, while biologically active dimeric FSH and LH can be produced by the human fetal pituitary by 14 weeks, dimeric biologically active TSH will only be produced from around 17 weeks of gestation. The mechanism(s) responsible for the different molecular regulation of alpha-GSU gene expression in gonadotropes and thyrotropes in the developing human fetal pituitary now requires investigation.     

Progestin receptors in dispersed rat anterior pituitary cells: Enriched binding in lactotrope fractions

Cytosolic progesterone and R5020 binding activities were demonstrated in Pronase-dispersed anterior pituitary cells from estrogenprimed ovariectomized and adrenalectomized rats. Pronase-dispersed pituitary cells were also separated into six cellular fractions on the basis of size and density by sedimentation velocity at unit gravity 1n a BSA gradient. Fractions enriched in lactotropes or gonadotropes were identified by the cellular contents of radioimmunoassayable prolactin and LH, respectively. Cytosollc progestin receptors appeared to be predominantly associated with lactotrope-rich fractions. Since there was some cross-over between the LH and prolactin enriched fractions, progestin receptors may also be associated with a subpopulation of gonadotropes, as well.     

Endogenous thyrotropin-releasing hormone in the anterior pituitary: sites of activity as identified by immunocytochemical staining.

Thyrotropin-releasing hormone (TRH) immunoreactivity was localized in the rat anterior pituitary with rabbit anti-TRH sera and the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique. Stain was present in secretory granules of cells possessing morphological characteristics of thyrotropes, gonadotropes and lactotropes. Antibody absorption studies with anti-TRH sera absorbed with TRH, 3 diastereoisomeric analogues of TRH, gonadotropin-releasing hormone (GnRH), bovine serum albumin, thyrotropin, prolactin, adrenocorticotropin, luteinizing hormone, follicle stimulating hormone were performed to determine the specificity of the staining reaction. Only absorption with TRH resulted in a significant reduction in staining intensity. In vitro experiments were then begun with hemipituitaries to ascertain if intrapituitary TRH might originate by sequestration of exogenous, plasma membrane bound TRH or by de novo synthesis. The results suggest that anterior pituitary TRH is of endogenous origin.     

Immunohistochemical characterization of chicken pituitary cells containing the vasotocin VT2 receptor

Research in mammals has demonstrated a variety of regulatory effects of vasopressin and oxytocin on endocrine functions of the anterior pituitary gland. Less evidence is available regarding the hypophysiotropic action of arginine vasotocin (AVT) comprising vasopressic and oxytocic activities in birds. Some hypophysiotropic effects of AVT may result from its interactions with brain circuits controlling pituitary functions, whereas others are caused by its direct affect on pituitary cells. Use of an antiserum to the vasotocin receptor VT2 (VT2R) has revealed numerous immunoreactive cells in the anterior pituitary gland of the chicken. The objective of the present study has been to identify endocrine phenotypes of chicken pituitary cells containing VT2R by means of immunohistochemical labeling. VT2R immunoreactivity has been found in all cells immunoreactive for adrenocorticotropin and alpha-melanotropin. Approximately 10% of labeled lactotropes are also immunoreactive for VT2R and lie around the anatomical boundary dividing the cephalic and caudal lobes. In both corticotropes/melanotropes and lactotropes, immunoreactive VT2R is present in a narrow layer outlining cell bodies. Immunoreactive VT2R is not found in gonadotropes, thyrotropes, or somatotropes. These results provide evidence for the important role of VT2Rs in mediating effects of AVT on endocrine secretion from corticotropes and, partially, from lactotropes.     

Localization and quantification of hormones, ligands, and mRNA with affinity-gold probes

The application of immunogold techniques to localize pituitary hormones produces label that can be quantified and correlated with different secretory states. This report focuses on three major applications of the technology. In the first set of studies, immunogold labels for adrenocorticotropin (ACTH) or luteinizing hormone (LH beta) and follicle-stimulating hormone (FSH beta) were applied to ultrathin sections of pituitaries from adrenalectomized rats or from rats in different stages of the estrous cycle. During the first week after adrenalectomy, ACTH cell area increased. The concentration of immunoperoxidase label (amount of label/area of the corticotropes) decreased. Counts of gold markers showed that there were no changes in the concentration of antigens per granule. Three weeks after adrenalectomy, the amount of immunoperoxidase label increased along with the concentration of that label. The concentration of gold label for ACTH on granules also increased. All changes correlated well with increases in serum ACTH stimulated by adrenalectomy. In the studies of cycling rats, gonadotropes showed increases in the number of gold markers for LH beta or FSH beta per granule area just before an elevation in serum levels. There were also increases in the proportion of granules that contained only LH beta or FSH beta (monohormonal) before the rise in secretion. Thus, nonparallel release of gonadotropins might be attributed to changes in the ratio of gonadotropins packaged per granule. In the second series of studies, avidin-gold labels were used to identify sites of binding of biotinylated ligands. These studies illustrate and quantify binding by biotinylated gonadotropin-releasing hormone (GnRH) to ovarian or pituitary target cells. Triple-labeling protocols (avidin-peroxidase followed by immunogold) show that the target cells in the pituitary contain gonadotropins. In the third set of studies, avidin gold or avidin peroxidase was used to label sites of hybridization of a biotinylated cRNA probe to gonadotropin beta subunit mRNA. The sites of hybridization appear on rough endoplasmic reticulum; however, further work is needed to improve cell ultrastructure and perserve antigens. Triple-labeling protocols (avidin-peroxidase followed by immunogold) show the feasibility of the technique as well as the need for further refinement. To summarize, these studies describe multiple applications of gold labels for the localization of antigens, ligands, and mRNA. The labels are sensitive for detection of antigens and ligands and easily quantified. Quantitative analyses show changes in concentration of gold label that correlate well with secretory states.     

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.     

Immunocytochemical localization of secretogranin III in the anterior lobe of male rat pituitary glands.

Secretogranin III (SgIII) is one of the acidic secretory proteins, designated as granins, which are specifically expressed in neuronal and endocrine cells. To clarify its precise distribution in the anterior lobe of the rat pituitary gland, we raised a polyclonal antiserum against rat SgIII for immunocytochemical analyses. By immunohistochemistry using semithin sections, positive signals for SgIII were detected intensely in mammotropes and thyrotropes, moderately in gonadotropes and corticotropes, but not in somatotropes. The distribution pattern of SgIII in the pituitary gland was similar to that of chromogranin B (CgB), also of the granin protein family, suggesting that the expressions of these two granins are regulated by common mechanisms. The localization of SgIII in endocrine cells was confirmed by immunoelectron microscopy. In particular, secretory granules of mammotropes and thyrotropes were densely and preferentially co-labeled for SgIII and CgB in their periphery. Moreover, positive signals for SgIII were occasionally found in cells containing both prolactin and TSH in secretory granules. These lines of evidence suggest that SgIII and CgB are closely associated with the secretory granule membrane and that this membrane association might contribute to gathering and anchoring of other soluble constituents to the secretory granule membrane.     

Fasting and glucose effects on pituitary leptin expression: is leptin a local signal for nutrient status?

Leptin, a potent anorexigenic hormone, is found in the anterior pituitary (AP). The aim of this study was to determine whether and how pituitary leptin-bearing cells are regulated by nutritional status. Male rats showed 64% reductions in pituitary leptin mRNA 24 hr after fasting, accompanied by significant (30-50%) reductions in growth hormone (GH), prolactin, and luteinizing hormone (LH), and 70-80% reductions in target cells for gonadotropin-releasing hormone or growth hormone-releasing hormone. There was a 2-fold increase in corticotropes. Subsets (22%) of pituitary cells coexpressed leptin and GH, and <5% coexpressed leptin and LH, prolactin, thyroid-stimulating hormone, or adrenocorticotropic hormone. Fasting resulted in significant (55-75%) losses in cells with leptin proteins or mRNA, and GH or LH. To determine whether restoration of serum glucose could rescue leptin, LH, and GH, additional fasted rats were given 10% glucose water for 24 hr. Restoring serum glucose in fasted rats resulted in pituitary cell populations with normal levels of leptin and GH and LH cells. Similarly, LH and GH cells were restored in vitro after populations from fasted rats were treated for as little as 1 hr in 10-100 pg/ml leptin. These correlative changes in pituitary leptin, LH, and GH, coupled with leptin's rapid restoration of GH and LH in vitro, suggest that pituitary leptin may signal nutritional changes. Collectively, the findings suggest that pituitary leptin expression could be coupled to glucose sensors like glucokinase to facilitate rapid responses by the neuroendocrine system to nutritional cues.     

Changes in gonadotrope responsivity to gonadotropin releasing hormone during development of the rhesus monkey

To assess the changing responsiveness of pituitary gonadotropes to gonadotropin releasing hormone (GnRH) during development, 5 male and 5 female rhesus monkeys were studied. Three monkeys of each sex were tested periodically with a subcutaneous injection of 500 micrograms of GnRH dissolved in 50% polyvinylpyrrolidone (PVP) beginning at 2 to 4 weeks of age and continuing into young adulthood. The remaining 4 monkeys received injections of the vehicle (PVP) alone and served as controls. Serum concentrations of bioactive luteinizing hormone (LH) were determined by an interstitial cell testosterone bioassay, and follicle-stimulating hormone (FSH) levels were measured by radioimmunoassay. Baseline FSH levels in the 5 female neonatal monkeys were higher than those of the 5 male neonatal monkeys during the first 2 months of life. In both sexes, FSH concentrations decreased with age, and FSH was barely detectable by 6 months. Baseline LH values in the 5 female monkeys declined during the first 6 months of the study and were undetectable (less than 0.5 micrograms/ml) at 6 months of age. Baseline LH levels in 4 of the 5 neonatal males also declined to undetectable concentrations by 6 months of age. During the first 3 months of life, there was a striking increase in the serum concentrations of both LH and FSH following GnRH. Although the LH responses to GnRH (delta LH) were similar in males and females of comparable ages, the FSH responses (delta FSH) were considerably greater in the female monkeys. In the males, the delta LH exceeded the delta FSH, whereas in the females, the delta FSH were greater than the delta FSH. In both sexes, the delta LH and delta FSH generally were greatest in the youngest monkeys and decreased gradually with increasing age. By 6 months, the gonadotropin responses to GnRH either were undetectable (males) or very small (females). After 6 months there was no longer an increase in serum gonadotropins after GnRH in either sex until 1.5-4 years (females) or 3 years (males) of age. The delta LH in response to GnRH in the male monkeys 3-5 years of age were comparable to the responses during the first month after birth. Serum concentrations of FSH in the adult males, however, did not increase after GnRH. In the female monkeys, serum levels of LH and FSH increased after GnRH at 1.5 years (1 monkey) and 4 years (2 monkeys) of age. The delta LH were similar to those of the 1- to 2-month-old female monkeys. The delta FSH, however, were variable and were approximately 20% of the neonatal response. In these young adult female monkeys the delta LH exceeded the delta FSH.(ABSTRACT TRUNCATED AT 400 WORDS)