Hypothalamic Stimulation of Insulin Release

Abstract

We have reported that the mouse ventro-lateral hypothalamus releases a humoral factor in vitro which stimulates insulin secretion by isolated islets (Idahl & Martin, 1971). We report here similar studies extended to rats, and attempts to isolate this hypothalamic factor and to demonstrate its presence in blood.Ventro-lateral (VLH) and ventro-medial hypothalami (VMH) of 16 rats were separated and extracted with 3 ml Gey & Gey (1936) buffer at 37 \ s=deg\ Cfor 30 min. Aliquots (0\m=.\4ml) of the extract were tested for stimulatory capacity by incubation (20 min at 37 \ s=deg\ C) with five islets of Langerhans. The incubation medium contained glucose (3\m=.\3 mmol/l and albumin (1 mg/ml), in a final volume of 0\m=.\5 ml Gey & Gey buffer. The amount of insulin released into the medium was compared with the amount released by the same islets during a preliminary 20-min incubation in a medium without the extract (baseline). Insulin concentration was measured by immunoassay (Herbert, Lau, Gottlieb & Bleicher, 1965). Results of a typical experiment, expressed in ng insulin/islet incubated for 20 min, were (mean and range of five observations): baseline, 2-0 (1-5-2-6); islets in VLH extract, 5-9 (3-8-8-4); islets in VMH extract, 1-8 (0-5-2-6). The VLH extract stimulated insulin release while the VMH extract had no effect. Isolation of this islet-stimulating material was attempted by fractionation of the VLH extract through a Sephadex G-100 column. Figure la shows that the islet-stimulating activity resides in fractions in the descending portion of the second peak.The presence of the islet-stimulating factor in plasma was examined by passing dialysed rat plasma through a Sephadex G-100 column, as shown in Fig. 16: the fractions eluted in the shoulder of the albumin peak stimulated insulin release. The elution volume of this fraction was identical with that of the active fraction from the VLH extract. Further purification ofthis fraction by acrylamide gel electrophoresis and electrofocusing is in progress.The VLH origin of the plasma material was indicated by the following experiment : plasma from normal rats and from rats 48 h after the electrolytic destruction of the VLH (Steffens, Mogenson & Stevenson, 1972) were investigated for their islet stimu¬ lating capacity. Both normal and VLH-lesioned rats were tube-fed for 10 days before the operation and thereafter until the time of killing. The plasma was dialysed and 0-4-ml aliquots from each animal were tested. Table 1 shows that the plasma from the VLH-lesioned animals failed to stimulate the islets while the plasma from the controls remained fully active.

Dynamics of Glucose-Induced Plasma Insulin Increase in the Rat Fetus at Different Stages of Gestation

“…The possibility that a cephalic factor could be involved in the response of fetal /3-cell to glucose stimulation has been suggested by several observations: (a) the anencephalic new borns of diabetic women had a hyperinsulinemia only if their hypothalamo-hypophyseal system was intact (28); (b )a humoral hypothalamic islet-stimulating factor has been identified in adult rats (24), and (c) a hypo physeal factor that stimulates insulin secretion by the pancreas has been described in adult dog (8) and mice (5). Furthermore, it has also been proposed that a gastrointestinal factor could be involved in the maturation of the response of the fetal /3-cells to glucose (29).…”

Congenital Generalized Lipodystrophy and Experimental Lipoatrophic Diabetes in Rabbits Treated Successfully With Fenfluramine

“…The existence of such agents have been demonstrated. Martin et al (1973) isolated an agent which stimulated insulin secretion by isolated pancreatic islets in vitro, and Moltz et al (1975) an agent producing hyperglucagonaemia and reduction of serum insulin. The tridecapeptide neurotensin has been demonstrated to produce hyperglycaemia and increase of serum glucagon (Brown 8c Vale 1976).…”

Lipoatrophy Produced in Mice and Rabbits by a Fraction Prepared From the Urine From Patients With Congenital Generalized Lipodystrophy

“…The effect may possibly be related to an insulinotrophic factor isolated from rat and mouse hypothalami (Martin et al 1973). …”