Some species differences in cardiovascular responses to intravenously injected leucine-enkephalin

Role of limbic peptidergic circuits in regulation of arterial pressure, relevant to development of essential hypertension

It is generally accepted that the essential hypertension (EH) is caused by interactions among congenital gene, multiple pathogenetic pressor factors, and disorder of physiologic depressor factors. The central nervous system may play a key role in the development of EH. The underlying mechanisms, however, are not well understood. Studies show that peptidergic transmitters in the limbic forebrain are involved in long-term regulation of arterial pressure and in the pathogenesis of EH. In the limbic forebrain there are peptidergic pressor and depressor circuits. The former includes corticotropin releasing factor-, substance P-, and angiotensin II-circuits; and the latter includes beta-endorphin- and atrial natriuretic peptide-circuits. These circuits extensively interconnect and interact with each other. The altered functions of them may be the pathogenesis of EH. In this review, we focus on the roles of limbic peptidergic circuits in regulation of arterial pressure, relevant to the neurogenetic mechanisms in developing EH.

Distribution of leucine-enkephalin in bone and joint tissues

The distribution and concentration of leu-enkephalin in periosteum, cortical bone, bone marrow and synovial membrane of normal rats were analysed. Periosteum, cortical bone and bone marrow of the rat femurs were collected as well as the ankles. The distribution of leu-enkephalin was analysed by immunoelectron microscopy and the concentration of leu-enkephalin was measured with radioimmunoassay. Immunoelectron microscopy showed that leu-enkephalin is abundant in monocytes of bone marrow, nerve fibers and endothelial cells in the periosteum and also in macrophage-like-cells of the synovial membrane. The concentration of leu-enkephalin measured by RIA showed highest concentration in bone marrow followed by periosteum and cortical bone. The study supports that leu-enkephalin is present and can be quantified in different compartments of bone and joint tissues suggesting that leu-enkephalin may be involved in the physiological regulation of nociception and immunoregulation.

Effects of enkephalins and the analogue FK-33824 on mean arterial pressure and heart rate in conscious sheep

Experiments were designed to evaluate the central and systemic effects by enkephalins and the enkephalin analogue FK-33824 on mean arterial pressure (MAP) and heart rate (HR) in conscious sheep. Intracerebroventricular infusion of FK-33824 increased both MAP and HR in a dose-dependent manner in normal sheep. The increases in MAP and HR were attenuated by naloxone administered centrally, but not systemically. Intracerebroventricular infusion of met-enkephalin, leu-enkephalin and naloxone failed to change both MAP and HR significantly. However, intravenous infusion of met-enkephalin, leu-enkephalin and FK-33824 resulted in bradycardia. Haemorrhage alone decreased both MAP and HR. Intracerebroventricular infusion of FK-33824 blunted the reduction in MAP in response to haemorrhage. The increases in MAP and HR following FK-33824 were also accompanied by elevated levels of plasma renin concentration. It is suggested that the tachycardia and pressor effect produced by the intracerebroventricular administration of FK-33824 in normal conscious sheep may result from a combined action of both neural and chemical pathways which are involved in cardiovascular control, and are mediated via the mu-opioid receptors. Opioids may have opposite effects on cardiovascular control depending on the route of administration.

Copper deficiency in rats increases pancreatic enkephalin-containing peptides and insulin

Free enkephalins (enk) and higher molecular weight enkephalin-containing peptides (enk-c-p) are present in the endocrine pancreas of rats, presumably in B cells. To determine whether these opioid peptides show dynamic alterations as insulin content of pancreas changes, we utilized a copper deficient rat model, in which the exocrine pancreas atrophies and the endocrine pancreas is "intact" and insulin (IRI) content increases. Dietary copper deficiency (-C) was produced in weanling male rats for 4 and 7 weeks. The deficient and copper supplemented (+C) groups were further subdivided to receive all dietary carbohydrate as either 62% fructose (F) or 62% starch (S). -CF rats showed the most severe deficiency. After 7 weeks, total units of pancreatic IRI in -CF were 7.5 +CF 2.1, -CS 7.9 and in +CS 2.8 (p less than 0.001). Pancreatic content of Met5- and Leu5-enk was measured in extracts which were purified on C-18 Seppaks with and without prior treatment with trypsin and carboxypeptidase B. -C animals showed progressive, significant increases in pancreatic content of Leu-enk-c-p, with a decrease in free Leu- and Met-enk (p less than 0.02-0.01). The pancreatic findings are compatible with a co-localization of enkephalins and insulin in the endocrine pancreas and are suggestive of co-regulation.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.