Effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on hormone secretion from sheep pituitary cells in vitro

Although vasoactive intestinal polypeptide (VIP) is thought to be a prolactin releasing factor, in vivo studies on sheep suggest that it is inactive in this species. Recent studies, based primarily on the rat, suggest that the related pituitary adenylate cyclase-activating polypeptide (PACAP) is also a hypophysiotrophic factor but again in sheep, this peptide has no in vivo effects on hormone secretion despite being a potent activator of adenylate cyclase in vitro. This lack of response to either peptide in vivo in sheep could be due to the low concentration of peptide that reaches the pituitary gland following peripheral injection. In the present study we therefore adopted an alternative approach of evaluating in vitro effects of these peptides on GH, FSH, LH or prolactin secretion from dispersed sheep pituitary cells. In a time-course study, PACAP (1 mu mol/l) increased GH concentrations in the culture medium between 1 and 4 h and again at 12 h but had no effect in the 6 and 24 h incubations. Prolactin, LH and FSH were not affected by PACAP. The response to various concentrations of PACAP (1 nmol/l-1 mu mol/l) were then evaluated using a 3 h incubation. Again prolactin and LH were not affected by PACAP and there was a small increase in GH concentrations but only at high concentrations of PACAP (0.1 and 1 mu mol/l; P<0.05), PACAP also stimulated FSH secretion in cells from some animals although this effect was small, The GH response to PACAP was inhibited by PACAP(6-38), a putative PACAP antagonist; but not by (N-Ac-Tyr(1), D-Arg(2))-GHRH(1-29)-NH2, a GH-releasing hormone (GHRH) antagonist. The cAMP antagonist Rp-cAMPS was unable to block the GH response to PACAP suggesting that cAMP does not mediate the secretory response to this peptide. At incubation times from 1-24 h, VIP (1 mu mol/l) had no effects on prolactin, LH or GH secretion and, in a further experiment based on a 3 h incubation, concentrations of VIP from 1 nmol/l-1 mu mol/l were again without effect on prolactin concentrations. Interactions between PACAP and gonadotrophin releasing hormone (GnRH), GHRH and dopamine were also investigated. PACAP (1 nmol/l-1 mu mol/l) did not affect the gonadotrophin or prolactin responses to GnRH or dopamine respectively. However, at a high concentration (1 mu mol/l), PACAP inhibited the GH response to GHRH. In summary, these results show that PACAP causes a modest increase in FSH and GH secretion from sheep pituitary cells but only at concentrations of PACAP that are unlikely to be in the physiological range. The present study confirms that VIP is not a prolactin releasing factor in sheep.

Imunofluorescência para neuropeptídeos na mucosa nasal humana: avaliação de técnica para peptídeo intestinal vasoativo (VIP)

Os neuropeptídeos são neurotransmissores relevantes na fisiologia nasal e o conhecimento crescente acerca de seu papel na fisiopatologia de doenças nasais abre novas perspectivas. A sua investigação na mucosa nasal humana baseia-se em grande parte em marcação imunológica, método complexo e sujeito a inúmeros fatores de erro. Com o intuito de viabilizar este tipo de pesquisa em nosso meio, um método de imunofluorescência para peptídeo intestinal vasoativo (VIP) na mucosa nasal humana é proposto e avaliado. FORMA DE ESTUDO: Coorte transversal. MATERIAL E MÉTODO: Oito pacientes submetidos a cirurgia funcional do nariz têm um fragmento de mucosa coletado da concha inferior. O tecido foi fixado em solução de Zamboni (paraformaldeído 4% tamponado e ácido pícrico 0,4%), congelado em nitrogênio líquido e armazenado. Cortes de 14 µm foram realizados e submetidos à reação de imunofluorescência para VIP (Península Laboratories). As imagens microscópicas foram documentadas em fotografia convencional. A especificidade, sensibilidade e reprodutibilidade de execução foram avaliadas. A reprodutibilidade de interpretação de resultados foi avaliada através da comparação de graus de marcação (0 a 4) atribuídos às fotos por seis observadores. RESULTADOS: Os resultados mostraram ser o método suficientemente específico, sensível, além de reprodutível em sua execução. A interpretação de resultados mostrou depender do perfeito esclarecimento do observador no julgamento das imagens de imunofluorescência, mas mostrou uniformidade. CONCLUSÃO: O método proposto foi considerado útil na pesquisa de neuropeptídeos na mucosa nasal humana.

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