Development of insulin and epidermal growth factor receptors during the differentiation of rat preadipocytes in primary culture.

An homogeneous cell population isolated from the inguinal tissue of 3-day-old rats is able to proliferate in primary culture. In the presence of a physiological concentration of insulin (1.5 nM) it converts into cells exhibiting the morphology and the biochemical characteristics of adipocytes. Insulin and epidermal growth factor (EGF) receptors were studied during both the exponential growth and the adipose conversion phases of these cells. Binding experiments with 125I-labelled peptides were performed directly in the culture dishes. The number of high affinity insulin binding sites increased, during the entire culture period studied, reaching 18 days after plating the value of 10,600 x 2360. Control cells (cultured in the presence of anti-insulin antibody) exhibited an increase of the concentration of insulin binding sites from no more than 500 sites/cell to 6880 +/- 1710 sites/cell between dat 0 and 9 (corresponding to the exponential growth phase); this increase was followed by a rapid reduction in insulin receptors during the stationary phase. The density of EGF binding sites increased between day 0 and 4 (one cell cycle), whether the cells were maintained or not with insulin, and plateaued thereafter. Mature adipocytes freshly isolated from the inguinal tissue of 3-day-old rats had no detectable EGF binding sites, but their content in high affinity binding sites for insulin was similar to that of cells after complete adipocyte conversion in primary culture.

[Characterization and differentiation of rat preadipocytes in primary culture]. / Caractérisation et différenciation de préadipocytes de rats en culture primaire.

Using a density gradient medium, we isolated homogeneous cell populations from the inguinal tissue of 3-day old rats. In primary culture we obtained, for the first time, the differentiation of 99% of the cells in the presence of a physiological concentration of insulin (10(-9) M). This model closely mimicked the events occurring during normal mammalian adipose development, i.e. a positive change in beta-adrenergic sensitivity, early induction of lipoprotein lipase, expression of the enzymes involved in the triglyceride systems, and the development of responsiveness to glucagon.

Release of vasoactive intestinal peptide from rat jejuno-ileum in vitro. Effect of various depolarizing agents.

Vasoactive intestinal peptide (VIP) can be released in vitro from intestinal slices under veratridine and batrachotoxin depolarization, whereas potassium depolarization has no effect. The lack of an effect of potassium observed in this peripheral preparation is different from the positive action described for it in the CNS. The present data suggest that VIP can be released through different mechanisms in the peripheral and central nervous system.

Release of vasoactive intestinal peptide from rat brain slices by various depolarizing agents.

The release of vasoactive intestinal peptide (VIP) from rat brain cortical and amygdala slices was studied by using various depolarizing agents such as potassium (K+), veratridine (VER) and batrachotoxin (BTX). The basal release of VIP observed is of the same order of magnitude for both structures and represents less than 0.1% of the tissue content per minute measured by a specific radioimmunoassay. Maximal stimulation obtained with 56 mMK+, 50 microM VER and 1 microM BTX corresponds to a mean 3-fold increase above the basal release of VIP in both cortex and amygdala. When the incubation medium did not contain any calcium, the action of potassium on the release of VIP was suppressed. When tetrodotoxin (1 microM) was added to the incubation medium, the veratridine- and batrachotoxin-induced release of VIP was inhibited whereas K+-induced release was unaffected. These results support the hypothesis that VIP can be a neurotransmitter in the central nervous system.