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
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A Cell
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α Adrenergic Receptors
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Plasma Glucagon
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Glucose Free Fatty Adds
