Daily rhythm of glucose‐induced insulin secretion by isolated islets from intact and pinealectomized rat

Abstract

It is well known that pinealectomy induces in rats a diminished glucose tolerance, insulin resistance, a reduction in GLUT4 content in adipose and muscular tissues, a decrease in hepatic and muscular glycogenesis, impairment of glucagon action and an increase in blood pyruvate concentration. In addition, it has been shown that melatonin suppresses insulin secretion in several experimental conditions. The objective of the present study was to investigate the daily rhythm of glucose-induced insulin secretion and glucose oxidation by isolated pancreatic islets and to investigate the effect of chronic absence of melatonin (30 days of pinealectomy) on this rhythmic process. The data obtained confirmed the presence of a strong 24-hr rhythm of insulin secretion by isolated pancreatic islets. In addition, it was demonstrated that the glucose-metabolizing ability of the B-cell follows a daily rhythm phase locked to insulin secretion rhythm. Most interesting, however, was the demonstration that the daily rhythmic processes of insulin secretion and B-cell -[U-14C]-glucose oxidation by isolated pancreatic islets is completely modified by the chronic absence of the pineal gland. Thus, pinealectomy induced in all groups an increase in 24-hr mean glucose-stimulated insulin secretion and [U-14C]-glucose oxidation, in addition to some alterations in the rhythmic amplitude and a remarkable phase-advancing of the daily curves for 8.3 mm glucose (a condition similar to that observed in fed animals and where the B-cells are supposedly more active). These observations strongly suggest that the presence of the pineal gland may be necessary for the proper synchronization of these metabolic rhythms with other circadian rhythms like activity-rest and feeding.

Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

“…Consistent experimental results in laboratory rats show that the absence of rhythmic release of melatonin in blood circulation leads to chronodisruption of functions associated with energy metabolism. In particular pinealectomy, suppressing the nocturnal rise in melatonin, disturbs the 24 h rhythm of plasma glucose concentration (la Fleur et al, 2001b) and eliminates the daily rhythm of glucose-induced insulin secretion (Picinato et al, 2002). In addition, impaired glucose tolerance, decreased adipose cell responsiveness to insulin and a reduction in GLUT4 content in muscle and adipose tissue have been reported after pinealectomy (Lima et al, 1998).…”

Wydzielanie serotoniny i melatoniny u kobiet po menopauzie z zaburzeniami odżywiania

“…First research studies revealed that secretion of melatonin was higher in women with both anorexia nervosa and bulimia than in the control groups [12]. However, experimental studies demonstrated increased insulin resistance, development of glucose intolerance, and weight gain in pinealectomised rats [13]. It was also shown that melatonin supplementation in animals with induced obesity had a positive effect on the secretion of leptin and adiponectin and on the level of glucose, cholesterol, and triglycerides [14,15].…”

In vivo activation of insulin receptor tyrosine kinase by melatonin in the rat hypothalamus

“…In mammals, the physiological functions of melatonin are, among other mechanisms, regulation of the circadian clock in the hypothalamic suprachiasmatic nucleus (SCN), seasonal reproduction, and inhibition of dopamine release from the retina (Morgan et al 1994;Vanecek 1998). Experiments with pinealectomized animals demonstrated that melatonin also plays a role in energy expenditure, body mass regulation, and insulin peripheral action and secretion (Margraf and Lynch 1993;Lima et al 1998;La Fleur et al 1999;Picinato et al 2002). It has been demonstrated that the biological effects of melatonin are mediated, at least in part, by specific high-affinity G protein-coupled receptors (GPCRs).…”