Decreased content of immunoreactive enkephalin-like peptide in peripheral tissues of spontaneously hypertensive rats

Abstract

THE dopaminergic modulation of neuronal transmission in coeliac ganglia of spontaneously hypertensive rats (SHR) has been shown to be less efficient than in control Wistar Kyoto rats (WKY). From these results it was inferred that the development of hypertension may be due to this defect. Recent reports^2,3 suggest that polypeptides may function as neurotransmitters or neuromodulators in sympathetic ganglia. A heterogeneous group of immunoreactive Met⁵-enkephalin-like (ME) peptides have been found in these ganglia³, and are also present in adrenal glands, in both chromaffin cells and afferent axons (unpublished observations). Some of these peptides, when released from the afferent axons, may modulate opiate receptors located in adrenal medulla (unpublished observations). The vasodilatory action of morphine suggests that if the opiate agonists present in the chromaffin cells were to be secreted they might also cause vasodilation by acting on distant receptors. In view of their possible role in the regulation of sympathetic transmission and vascular tone, we have studied the content and Chromatographie characteristics of the immunoreactive ME-like peptides in adrenal gland, sympathetic ganglia, salivary gland and hypothalamus of SHR and WKY rats. We report here that the content of these peptides was lower in SHR than WKY rats in all tissues studied, except the hypothalamus. In sympathetic ganglia this decrease was due to a reduction in the ME content and not to that of the high molecular weight (MW) immunoreactive ME-like peptides.