Localization, characterization and activity of pituitary adenylate cyclase-activating polypeptide in the frog adrenal gland

Abstract

Pituitary adenylate cyclase-activating polypeptide (PACAP) has recently been isolated from the frog brain and the sequence of the peptide appears to be strikingly similar to that of mammalian PACAP. In the present study, we have investigated the localization of PACAP in the frog interrenal (adrenal) gland by immunocytochemistry using antisera directed against PACAP 38 or PACAP 27. Two types of PACAP-immunoreactive fibres were observed: thick varicose fibres coursing between adrenal cells and thin processes located in the walls of blood vessels irrigating the gland. Bilateral transection of the splanchnic nerves did not affect the intensity and distribution of PACAP immunoreactivity. The mean +/- S.E.M. concentration of PACAP, measured by radioimmunoassay in crude adrenal extracts, was 0.65 +/- 0.16 nmol/g wet tissue. Two molecular forms of PACAP in the adrenal gland were characterized by reversed phase high-performance liquid chromatography combined with radioimmunoassay quantification. The elution profiles revealed the existence of two peaks exhibiting the same retention times as synthetic frog PACAP 38 (fPACAP 38) and PACAP 27, the predominant form being PACAP 38. The possible involvement of PACAP in the regulation of adrenal steroidogenesis was investigated in vitro using a perifusion system for frog adrenal slices. Graded doses of fPACAP 38 (0.1-10 mumol/l) increased the secretion of both corticosterone and aldosterone in a dose-dependent manner. Administration of repeated pulses of fPACAP 38 (1 mumol/l), at 120-min intervals, led to a reproducible stimulation of corticosteroid secretion without any tachyphylaxis. Prolonged infusion (2 h) of the peptide induced a rapid increase in corticosterone and aldosterone output, followed by a gradual decline in the secretion rate, suggesting the occurrence of a desensitization phenomenon. Synthetic porcine vasoactive intestinal peptide, which is structurally related to PACAP, was about ten times less potent than fPACAP 38 in stimulating steroidogenesis while the [Des-His1]-fPACAP 38 analogue was 100 times less effective. These results demonstrate that a peptide closely related to fPACAP 38 is present in fibres innervating the frog adrenal gland and could participate in the regulation of corticosteroid secretion, particularly during neurogenic stress.

Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) in the frog (Rana ridibunda) tadpole brain: Immunohistochemical localization and biochemical characterization

“…Consistent with this observation, it has been previously shown that PACAP38 is the major molecular form occurring in the brain of mammals and fish . Similarly, predominance of PACAP38 over PACAP27 has been reported in the frog adrenal gland (Yon et al, 1993b) and in the adrenal gland of human fetuses (Breault et al, 1998). In tadpole brain extracts, a minor immunoreactive peak coeluting with synthetic PACAP27 was also detected, suggesting that a small proportion of PACAP38 is processed by prohormone convertases (PC) to generate PACAP27.…”

“…The concentrations of PACAP-like material in tadpoles brains extracts and in HPLC fractions were measured by RIA as previously described (Yon et al, 1993b). Iodination of synthetic PACAP27 was performed by means of the lactoperoxidase technique (Laquerrière et al, 1989).…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…In mammals, PACAP is found in the adrenal medulla (Shiotani et al, 1995), where it is contained both in chromaffin cells (Holgert et al, 1996) and in fibers (Frödin et al, 1995;Moller and Sundler, 1996;Tornøe et al, 2000). In the Italian wall lizard, Podarcis sicula, PACAP and its mRNA are detected in chromaffin cells, whereas in the frog adrenal gland, PACAP-LI is restricted to nerve fibers that contact either chromaffin cells or steroid-producing cells (Yon et al, 1993a;Valiante et al, 2008). It has been suggested that in the rat and dog adrenal gland, PACAP released from nerve endings contributes to neurally evoked catecholamine release (Fukushima et al, 2001a;Lamouche and Yamaguchi, 2003).…”

Regulation of Growth Hormone Release in Common Carp Pituitary Cells by Pituitary Adenylate Cyclase-Activating Polypeptide: Signal Transduction Involves cAMP- and Calcium-Dependent Mechanisms

“…Within the central nervous system, PACAP is known to function as a neurotransmitter [12], neurotrophic factor [13], and hypophysiotropic modulator [14]. In the periphery, PACAP regulates gut motility [15], dilation of airway [16], vasoconstriction [17], insulin secretion [18], and steroid production in the ovary [19]and adrenal gland [20]. The biological actions of PACAP can be mediated by three different receptor subtypes, namely PAC-1, VPAC-1 and VPAC-2 receptors [21].…”