Modulation by the Nutritional State of Adrenergic Receptor Mediated Effects on Insulin Secretion in Ducks

Summary

The effects of exogenous (IV Norepinephrine (NE)) and endogenous α adrenergic activity (IV phentolamine (PH)) were studied in the duck. Our aim was first to compare their importance in animals fed for 1 1/2 hours and fasted for 24 and 48 hours, and then to assess the relative importance of α versus β adrenergic receptor mediated effects during the development of a 48-hour-fast. NE reduces plasma IRI levels after a fast but not in the postprandial state. PH while ineffective in animals fed for 1 1/2 hours brings fasting IRI values to levels observed in the former group. Twenty-four hour fasted ducks are sensitive to both α adrenergic stimulation and β adrenergic blockade which have additive effects; so, insulin secretion is controlled by 2 distinct mechanisms: a β stimulating and an α inhibiting one. The importance of one component versus the other is modulated by the nutritional state: indeed, a double α and β equimolar adrenergic blockade reveals that during the transition from the postprandial state to a 48-hour-fast, there is a progressive reversal in the importance of one adrenergic component versus the other. The effects of α adrenergic stimulation or blockade occur independently of simultaneous glucose variations. This is not the case for A cell function: an α adrenergic receptor stimulating effect on glucagon secretion exists, but A cell remains primarily sensitive to plasma glucose level. α adrenergic activity has no direct effect on plasma free fatty acids (FFA) level but plays a role in plasma glucose level regulation especially in animals in the postprandial state.

Key-Words:

B Cell - A Cell - α Adrenergic Receptors - Plasma Glucagon - Glucose Free Fatty Adds