Influence of the pineal gland on the physiology, morphometry and morphology of pancreatic islets in rats

Abstract

To investigate the influence of the pineal gland through melatonin secretion on the physiological and morphological parameters of pancreatic islets, we studied the plasma biochemistry and morphological and morphometric characteristics of the endocrine pancreas of male Wistar rats. The animals were distributed into five groups of ten rats each: NC -normal control group; NS -sham-operated group; Px (25) -pinealectomised group, studied 15-25 days after surgery; Px (70) -pinealectomised group, studied 60-70 days after surgery; ALX -alloxan monohydrate-treated group. Data are analyzed statistically by ANOVA and by the Kruskal-Wallis test. Although there was no significant difference in plasma glucose or insulin levels between the Px (25), Px (70) and NC groups, Px (25) animals showed a tendency to increased glucose and reduced insulin levels. The ALX group showed a clear elevation of plasma glucose and a reduction of plasma insulin compared to the other groups. Morphometric analysis showed a larger pancreatic islet area and a lower pancreatic islet density in the pancreas of Px (70) animals and an increase in degenerative pathological processes in the pancreatic islets of the Px (25) and ALX groups. The present results suggest that melatonin, in addition to acting on tissue sensitivity to insulin (as reported in other studies), affects the secretory action of beta cells, as demonstrated by the morphological and morphometric changes observed in pinealectomised animals.Key words: pinealectomy, melatonin, pancreatic islet, rat, morphology. RESUMOA influência da glândula pineal na fisiologia, morfometria e morfologia das ilhotas pancreáticas em ratosCom o objetivo de verificar a influência da glândula pineal, por meio da secreção de melatonina (MLT) sobre a morfologia, morfometria e fisiologia das ilhotas de Langerhans (IP), especialmente sobre a secreção e ação da insulina, foram avaliados o metabolismo, a bioquímica plasmática, a morfologia e a morfometria de segmentos de pâncreas de 50 ratos Wistar. Os animais foram distribuídos em cinco grupos de dez animais cada, sendo dois grupos controles: N (controle normal); CF (submetidos à cirurgia fictícia) e três grupos experimentais: P 1 (pinealectomizados e avaliados entre 15 e 25 dias pós-cirurgia); P 2 (pinealectomizados e avaliados entre 60 e 70 dias pós-cirurgia) e Alx (tratados com Aloxana). Os resultados obtidos dos grupos experimentais foram analisados estatisticamente por ANOVA e teste de Kruskal-Wallis e comparados com os obtidos do grupo N. Embora não houvesse diferença significativa nos níveis plasmáticos de glicose ou insulina entre os grupos P 1 , P 2 e N, os animais do grupo P 1 mostraram tendência de aumento da glicose e níveis reduzidos de insulina. O grupo Alx mostrou elevação da glicemia e redução da insulinemia em relação aos demais grupos. A análise morfométrica revelou maior área e menor densidade das IP nos segmentos dos pâncreas do grupo P 2 . Em relação à análise morfológica, observou-se maior intensidade dos processos patológicos degenerati...

Melatonin and Pancreatic Islets: Interrelationships between Melatonin, Insulin and Glucagon

“…Pinealin increases glucose tolerance, whereas pinealectomy decreases insulin secretion and glucose tolerance [6,10,11]. These results are in accordance with later findings of the Spanish group of Blásques et al [12–14] who indicated that pinealectomy or bilateral sympathetic denervation of the pineal gland significantly reduces insulin levels and increases blood glucose [15–18]. These effects could be counteracted by melatonin application [19].…”

Chronomedicine and type 2 diabetes: shining some light on melatonin

“…This temporal relationship presents a unique challenge to understanding the mechanisms whereby melatonin affects glucose metabolism. In addition to this dichotomy, we find that melatonin can have conflicting impacts on target tissues, such as the pancreatic beta cell, in both rodents and humans [49,111,140], and highly variable effects on systemic glucose homeostasis and insulin sensitivity [28,29,111,141,142]. In vitro, melatonin inhibits insulin secretion by lowering cAMP and cGMP production [27,49,[143][144][145].…”

Effect of melatonin on biochemical variables of the blood in dairy cows

“…It stimulates this process in the liver (Haagsmann et al, 1981;Cardonigra-Valino et al, 1997;Bremmer et al, 1999). The action of pineal gland hormone on insulin level had been observed earlier by Peschke et al (1997), who suggested a direct action of melatonin on the pancreatic islets (de Lima et al, 2001). Maćkowiak et al (1999a) and Fabiś et al (2002) also showed an increase in the levels of insulin in rats along with the simultaneous increase in the level of glucose after the administration of exogenous melatonin.…”