Measurement of the secretion of a small peptide at the single cell level by the cell immunoblot assay: thyroidectomy increases the number of substance P-secreting anterior pituitary cells

Hypothalamic Contribution to Pituitary Functions Is Recapitulated In Vitro Using 3D-Cultured Human iPS Cells

The pituitary is a major hormone center that secretes systemic hormones responding to hypothalamus-derived-releasing hormones. Previously, we reported the independent pituitary induction and hypothalamic differentiation of human embryonic stem cells (ESCs). Here, a functional hypothalamic-pituitary unit is generated using human induced pluripotent stem (iPS) cells in vitro. The adrenocorticotropic hormone (ACTH) secretion capacity of the induced pituitary reached a comparable level to that of adult mouse pituitary because of the simultaneous maturation with hypothalamic neurons within the same aggregates. Corticotropin-releasing hormone (CRH) from the hypothalamic area regulates ACTH cells similarly to our hypothalamic-pituitary axis. Our induced hypothalamic-pituitary units respond to environmental hypoglycemic condition in vitro, which mimics a life-threatening situation in vivo, through the CRH-ACTH pathway, and succeed in increasing ACTH secretion. Thus, we generated powerful hybrid organoids by recapitulating hypothalamic-pituitary development, showing autonomous maturation on the basis of interactions between developing tissues.

Advent and recent advances in research on the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of gonadotropic hormone secretion of female rats

PACAP (ADCYAP1) was isolated from ovine hypothalami. PACAP activates three distinct receptor types: G-protein coupled PAC1, VPAC1, and VPAC2 with seven transmembrane domains. Eight splice variants of PAC1 receptor are described. A part of the hypothalamic PACAP is released into the hypophyseal portal circulation. Both hypothalamic and pituitary PACAP are involved in the dynamic control of gonadotropic hormone secretion. In female rats, PACAP in the paraventricular nucleus is upregulated in the morning and pituitary PACAP is upregulated in the late evening of the proestrus stage of the reproductive cycle. PACAP mRNA peak in the hypothalamic PVN precedes the LHRH release into the portal circulation. It is supposed that PACAP peak is evoked by the elevated estrogen on proestrous morning. At the beginning of the so-called critical period of the same day, PACAP level starts to decline allowing LHRH release into the portal circulation, resulting in the LH surge that evokes ovulation. Just before the critical period, icv-administered exogenous PACAP blocks the LH surge and ovulation. The blocking effect of PACAP is mediated through CRF and endogenous opioids. The effect of the pituitary-born PACAP depends on the intracellular cross-talk between PACAP and LHRH.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates release of somatolactin (SL)-α and SL-β from cultured goldfish pituitary cells via the PAC₁ receptor-signaling pathway, and affects the expression of SL-α and SL-β mRNAs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that stimulates the release of adenohypophyseal hormone from the pituitary in fish. In the goldfish, PACAP induces the release of somatolactin (SL), in particular, from cultured pituitary cells. SL belongs to the growth hormone and prolactin family, and comprises two molecular variants termed SL-α and SL-β in goldfish. However, there is no information about the involvement of PACAP in the regulation of SL-α and SL-β release and the expression of their mRNAs. Therefore, we examined the effect of PACAP on SL-α and SL-β release from cultured goldfish pituitary cells. Treatment with PACAP (10(-10)-10(-7)M) increased the release of both SL-α and SL-β. The stimulatory action of PACAP (10(-9)M) on SL-α and SL-β release was blocked by treatment with a PACAP-selective receptor (PAC1R) antagonist, PACAP(6-38) (10(-6)M). We also examined whether PACAP affects the expression of SL-α and SL-β mRNAs in cultured pituitary cells. Treatment with PACAP (10(-9) and 10(-8)M) for 6h decreased the expression level of SL-α mRNA but increased that of SL-β mRNA. The action of PACAP (10(-8)M) on SL-β mRNA expression was blocked by treatment with PACAP(6-38) (10(-6)M), whereas PACAP(6-38) elicited no change in the expression of SL-α mRNA. These results indicate that in cultured goldfish pituitary cells, PACAP stimulates the release of SL-α and SL-β, and expression of SL-β mRNA, via the PAC1R-signaling pathway. However, the mechanism whereby PACAP inhibits the expression of SL-α mRNA does not seem to be mediated by PAC1R signaling.

The octadecaneuropeptide stimulates somatolactin release from cultured goldfish pituitary cells

The present study aimed to investigate the distribution of the octadecaneuropeptide (ODN) in the goldfish brain and to look for a possible effect of ODN on somatolactin (SL) release from pituitary cells. A discrete population of ODN-immunoreactive neurones was localised in the lateral part of the nucleus lateralis tuberis. These neurones sent projections through the neurohypophyseal tract towards the neurohypophysis, and nerve fibres were seen in the close vicinity of SL-producing cells in the pars intermedia. Incubation of cultured goldfish pituitary cells with graded concentrations of ODN (10(-9) -10(-5 ) m) induced a dose-dependent stimulation of SL-β, but not SL-α, release. ODN-evoked SL release was blocked by the metabotrophic endozepine receptor antagonist cyclo(1-8) [DLeu(5) ]OP but was not affected by the central-type benzodiazepine receptor antagonist flumazenil. ODN-induced SL release was suppressed by treatment with the phospholipase C (PLC) inhibitor U-73122 but not with the protein kinase A (PKA) inhibitor H-89. These results indicate that, in fish, ODN produced by hypothalamic neurones acts as a hypophysiotrophic neuropeptide stimulating SL release. The effect of ODN is mediated through a metabotrophic endozepine receptor positively coupled to the PLC/inositol 1,4,5-trisphosphate/protein kinase C-signalling pathway.

Pituitary adenylate cyclase-activating polypeptide induces somatolactin release from cultured goldfish pituitary cells

In the goldfish pituitary, nerve fibers containing pituitary adenylate cyclase-activating polypeptide (PACAP) are located in close proximity to somatolactin (SL)-producing cells, and PACAP enhances SL release from cultured pituitary cells. However, there is little information about the mechanism of PACAP-induced SL release. In order to elucidate this issue, we used the cell immunoblot method. Treatment with PACAP at 10(-8) and 10(-7)M, but not with vasoactive intestinal polypeptide (VIP) at the same concentrations, increased the immunoblot area for SL-like immunoreactivity from dispersed pituitary cells, and PACAP-induced SL release was blocked by treatment with the PACAP selective receptor (PAC(1)R) antagonist, PACAP(6-38), at 10(-6)M, but not with the PACAP/VIP receptor antagonist, VIP(6-28). PACAP-induced SL release was also attenuated by treatment with the calmodulin inhibitor, calmidazolium at 10(-6)M. This led us to explore the signal transduction mechanism up to SL release, and we examined whether PACAP-induced SL release is mediated by the adenylate cyclase (AC)/cAMP/protein kinase A (PKA)- or the phospholipase C (PLC)/inositol 1,4,5-trisphosphate (IP(3))/protein kinase C (PKC)-signaling pathway. PACAP-induced SL release was attenuated by treatment with the AC inhibitor, MDL-12330A, at 10(-5)M or with the PKA inhibitor, H-89, at 10(-5)M. PACAP-induced SL release was suppressed by treatment with the PLC inhibitor, U-73122, at 3 x 10(-6)M or with the PKC inhibitor, GF109203X, at 10(-6)M. These results suggest that PACAP can potentially function as a hypophysiotropic factor mediating SL release via the PAC(1)R and subsequently through perhaps the AC/cAMP/PKA- and the PLC/IP(3)/PKC-signaling pathways in goldfish pituitary cells.

Effect of PACAP on LH release studied by cell immunoblot assay depends on the gender, on the time of day and in female rats on the day of the estrous cycle

We have previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) can be released from cultured rat anterior pituitary cells and when added to the medium in physiological concentration it releases LH from individual gonadotropes. In the present work, we studied whether the release of PACAP and the responsiveness of LH cells to PACAP depend on the gender, on the time of day when the animals were sacrificed, and in females on the stage of the estrous cycle. Anterior pituitary cells were cultured on nitrocellulose membrane. We found that the number of PACAP releasing cells was higher in proestrous than in diestrous female or in male rats and their number was always higher in the evening than at the other times. The effect of PACAP on LH cells was stimulatory in the morning of proestrus and diestrus. In proestrous rats, PACAP did not influence LH release in the afternoon or the evening, but in diestrous rats it decreased it in the afternoon and the evening. In males, there was a decrease of LH due to PACAP treatment at 10 and 20 h; however, PACAP did not influence LH at 16 h. It was concluded that in vivo PACAP might be involved in the circadian and episodic release of LH at pituitary level.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Intercellular communication in the anterior pituitary

In addition to hypothalamic and feedback inputs, the secretory cells of the anterior pituitary are influenced by the activity of factors secreted within the gland. The list of putative intrapituitary factors has been expanding steadily over the past decade, although until recently much of the work was limited to descriptions of potential interactions. This took the form of evidence of production within the pituitary of factors already known to influence activity of secretory cells, or further descriptions of actions on pituitary cells by such factors when added exogenously. A new phase of discovery has been entered, with extensive efforts being made to delineate the control of the synthesis and secretion of the pituitary factors within the gland, regulation of the receptors and response mechanisms for the factors in pituitary cells, and measurements of the endogenous actions of the factors through the use of specific immunoneutralization, receptor blockade, tissue from transgenic animals, and other means. Taken together, these findings are producing blueprints of the intrapituitary interactions that influence each of the individual types of secretory cells, leading toward an understanding of the physiological significance of the interactions. The purpose of this article is to review the recent literature on many of the factors acting as intrapituitary signals and to present such finding in the context of the physiology of the secretory cells.

Secretory activity of gonadotropin and the responsiveness of gonadotrophs to gonadotropin-releasing hormone during the annual reproductive cycle of male bats, Rhinolophus ferrumequinum: analysis by cell immunoblot assay

The purpose of this study was to examine secretory activity of gonadotropin (Gn) and the responsiveness of Gn secretion to Gn-releasing hormone (GnRH) in male horseshoe bats, Rhinolophus ferrumequinum, during the annual reproductive cycle. Anterior pituitary cells were monodispersed and subjected to cell immunoblot assay for Gn. Cell blots specific for follicle stimulating hormone (FSH) or luteinizing hormone (LH) were quantified using a microscopic image analyzer. The percentages of LH- or FSH-secreting cells detected as immunoreactive cell blots were markedly increased in the spermatogenic period (summer) and decreased in the hibernation period (winter). The mean Gn secretion from individual cells and total Gn secretion per unit area of the transfer membrane also showed similar changes. The responsiveness of Gn secretion to GnRH was greater in the spermatogenic period than in other seasons. On the other hand, although the secretory activity of Gn was markedly decreased during hibernation, a stimulatory effect of GnRH on Gn secretion was observed. These findings suggest that seasonal changes in the release of Gn required for gametogenesis and gonadal steroidogenesis varied depending on the reproductive activity and seasonal changes in Gn sensitivity to stimulatory effects of GnRH due to alterations in GnRH receptor numbers and/or in postreceptor events of gonadotrophs.

Matrix metalloproteinase-9 secretion by human pituitary adenomas detected by cell immunoblot analysis

Twenty-two pituitary adenomas were examined on the secretion of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) using a cell immunoblot assay, and discussed regarding an association between cavernous sinus invasion and the secretion of these proteins. The cell immunoblot assay, a kind of immunoblot procedure, is able to detect proteins at the single cell level and to detect the incidence of tumour cells secreting the target proteins in the total tumour cell population. The incidence of tumour cells secreting MMP-9 was significantly higher in invasive adenomas than in noninvasive ones. On the other hand, TIMP-1 secretion was not detected in any adenomas in this study. This result suggested that MMP-9 secretion, and especially the number of MMP-9-secreting cells, may be associated with cavernous sinus invasion of pituitary adenomas.