α-adrenergic, neurokinin and muscarinic receptors in rat mesenteric artery; An mRNA study during postnatal development

Developmental studies show that the innervation of autonomic targets is accompanied by increases in the density of receptors, maturation of receptor-signalling pathways and changes in receptor subtype. The innervation of the rat mesenteric artery occurs over the first 3 postnatal weeks. In this study, we investigated whether alterations in receptor gene expression may underlie physiological changes recorded during development and maturity in this vessel. Total RNA, from mesenteric arteries of rats at birth and postnatal days 7, 14, 28, 240 and 360, was reverse transcribed and amplified using primers specific for the α(1(A,B,D))- and α(2(A,B,C))-adrenergic, neurokinin (NK1-NK3) and muscarinic (m₁-m₅) receptors. Results showed that all receptor genes expressed at 28 days, except the α(1D)-adrenergic receptor, were already expressed at birth. Some receptor subtypes showed no change in their relative expression, always being either strongly (α(1A), α(2B), NK3) or weakly (α(2A), α(2C), NK1) expressed. Relative to the expression of these receptors, others showed a developmental increase in expression up to 14 days postnatal (α(1B), α(1D), m₂, m₃, m₅) but no further change with maturity. These latter changes coincide with the development of sympathetic and sensory nerve plexuses in the mesenteric artery, but do not correlate with the physiological changes seen during development and ageing.