Developmental changes in .ALPHA.-adrenergic and muscarinic receptor-mediated contractions of rat vas deferens.

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Abstract
Studies were made on developmental changes in phasic contractions of isolated rat vas deferens in response to norepinephrine (NE) and acetylcholine (ACh), which are mediated by α-adrenergic and muscarinic cholinergic receptors (α-R and m-R). The ED50 values of both contractions were almost constant during development, but the maximum responses to NE and ACh per wet weight and the relative contractions by NE and ACh to that by 100 mM K+ decreased greatly between 3 and 8 weeks after birth. However, the α- and m-receptors, assayed by measuring binding of [3H]-WB4101 and [3H]-quinuclidinyl benzylate (QNB), increased quantitatively per g wet weight and per mg protein between 2 and 8 weeks after birth, but did not change qualitatively. Thus, a discrepancy between the increases of α- and m-receptors and decreases of the maximum responses to NE and ACh was found, and possible mechanisms for this are discussed.