Co‐release of neuropeptide Y and catecholamines upon adrenal activation in the cat

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Abstract
The release of neuropeptide Y (NPY)‐like immunoreactivity (‐LI) in relation to catecholamines from the cat adrenal was studied in anaesthetized animals. Abdominal surgery increased plasma levels of NPY‐LI from 65± 6 to 149 ± 26 pmol 1‐1. A positive veno‐arterial concentration gradient over the adrenal gland was found for both NPY‐LI, adrenaline (Adr) and noradrenaline (NA) during basal conditions. Asphyxia for 2 min increased the output of both NPY‐LI and catecholamines from the adrenal. Electrical stimulation of the splanchnic nerve caused a marked increase in adrenal output of NPY‐LI and catecholamines. The adrenal content of NPY‐LI, as well as the release of NPY‐LI from the adrenal, was at least 1000‐fold lower on a molar basis than that of catecholamines. The concentration of NPY‐LI in the adrenal vein upon splanchnic nerve stimulation was in the nM range. Reversed‐phase HPLC characterization revealed that NPY‐LI in the adrenal, and in the adrenal venous plasma collected during splanchnic nerve stimulation, was closely related to synthetic porcine NPY. Stimulation with bursts of 20 Hz for 1 s with 10 s intervals for 2 min caused a four‐fold higher output of NPY‐LI and Adr compared to a continuous stimulation with 2 Hz, giving the same number of impulses. The NA output, however, was only slightly increased by burst stimulation. Guanethidine did not reduce the adrenal output of NPY‐LI or catecholamines induced by splanchnic nerve stimulation, while the release was abolished by chlorisondamine. NPY enhanced the in vitro contractile activity of Adr and NA on the a. profunda femoris from the cats used in the functional experiments. The threshold concentration of NPY for this enhancement was 250 pM. The NPY in higher concentrations (> 10‐8 M) had contractile effects per se. In conclusion, the present data suggest a functional relationship between adrenal release and effects of NPY and Adr.