Notes: 1. Synthetic human endothelin was injected intravenously over the range 1.5–50 μg to examine its cardiovascular actions in conscious sheep.2. Mean arterial pressure increased by 9–21 mmHg within 30–120s over the range 5–50 μg endothelin. The increase in blood pressure was associated with increased calculated total peripheral resistance and a fall in cardiac output and heart rate. Stroke volume was increased.3. Injection of endothelin into ganglion blocked sheep produced vasoconstriction and an increased blood pressure response associated with an attenuation of the effects on cardiac output, heart rate and stroke volume.4. This study suggests that endothelin produces potent arterial vasoconstriction and reflex mediated effects on the heart in conscious sheep.

Notes: 1. Synthetic human endothelin-1 was infused intravenously at 15 μg/h for 24 h to examine its cardiovascular actions in five conscious sheep.2. Endothelin produced a maximum increase in mean arterial pressure (MAP) of + 8 mmHg at 8 h, with an increase in calculated total peripheral resistance (CTPR) of +2.6 mmHg/L per min, whilst cardiac output (CO) was unchanged. At 24 h MAP was not significantly elevated, however CTPR had increased by +2.8 mmHg/L per min and CO had decreased by 0.9 L/min.3. This study shows that long-term administration of endothelin produces sustained arterial vasoconstriction in sheep.

Notes: 1. The haemodynamic and renal effects of short-term infusion of human atrial natriuretic peptide (ANP) (1–28) were examined in sheep treated with ACTH and compared with the responses previously observed in normotensive sheep.2. Infusion of ANP at 100 μg/h for 60 min in ACTH-treated sheep (5 μg/kg per day for 5 days) decreased blood pressure and produced a fall in both cardiac output and stroke volume. No changes were seen in heart rate and total peripheral resistance.3. ANP produced large increases in urine volume, urinary sodium and chloride excretion, and further decreased plasma potassium concentration in the ACTH-treated sheep. Compared with normal sheep studied previously under the same conditions, the ACTH-treated sheep showed a much greater diuretic and natriuretic response to ANP, although the blood pressure response to ANP was similar in both states.4. The change in renal responsiveness to ANP in sheep may be related to the increased blood volume of the ACTH-treated animals because volume expansion is known to enhance the renal effects of ANP.

Notes: Melanin concentrating hormone (MCH) is a 19 amino-acid peptide expressed in high concentrations within the dorso-lateral hypothalamus of rats, sheep and man. MCH regulates skin colour and ACTH release in teleost fish, however, its physiological relevance in mammals is unclear. The present study examined the cardiovascular and metabolic actions of intracerebroventricular (i.e.v.) infusion of MCH, and the pro-MCH derived peptide Neuropeptide-E-I (NEI), in conscious, chronically instrumented sheep. Human MCH (1–19) or NEI (1–13) was infused i.e.v. for 24 h into 6 sheep, and measurements were made every 10 min of arterial pressure, heart rate, cardiac output, stroke volume and peripheral blood flow/conductance. Recordings of water intake (H2Oin), urine volume (Uv), urinary Na (UNaV) and K excretion (UKV) were made, as well as hematocrit, plasma Na, K, osmolality, protein, glucose, ACTH, vasopressin, renin, endothelin, ANF, Cortisol and aldosterone concentrations. After 24 h of infusion at 10 μg/h, MCH produced a significant increase in Uv from 0.8 ± 0.2 to 1.4 ± 0.3 l/day, together with an increase in UNaV from 56 ± 8 to 107 ± 14 mmol/day, and in UKV from 202 ± 18 to 369 ± 38 mmol/day. H2Oin was unchanged. Similar renal changes were observed during i.e.v. infusion of NEI. There was no change in any cardiovascular parameter, although hematocrit showed a large decrease with infusion of both peptides after 24 h infusion. Plasma osmolality increased from 291 ±1 to 295 ± 1 mOsm/kg during MCH infusion, whereas total protein and plasma Na and K were unchanged. MCH increased plasma glucose from 3.4 ± 0.2 to 3.8 ± 0.2 mmol/l. Plasma aldosterone exhibited a 30–40% decrease following MCH or NEI infusion, whereas all other plasma concentrations remained unchanged. This study has shown that i.c.v. infusion of MCH or NEI can produce diuretic, natriuretic and kaliuretic changes in conscious sheep, triggered by a possible increase in plasma volume as indicated by the changes in hematocrit. These results, together with anatomical data reporting the presence of MCH/NEI in fluid regulatory areas of the brain, indicate that MCH/NEI may be an important peptide involved in the central control of fluid homeostasis in mammals.

Notes: The BE(2)-M17 and BE(2)-C human neuroblastoma cell lines have been shown to synthesize and secrete corticotropin-releasing factor (CRF) following retinoic acid treatment. It has been demonstrated that CRF secretion and intracellular synthesis increases in response to forskolin treatment. In this report, we have further characterized these cells in response to protein kinase C activators, dexamethasone, interleukin—1x, as well as various neurotransmitters and peptides. Nanomolar concentrations of the phorbol ester—phorbol 12 myristate 13—acetate (TPA), increased intracellular CRF content in both cell lines while increasing secretion only in the BE(2)-M17 cell. Nanomolar concentrations of dexamethasone were not able to alter basal levels of secretion and content in either cell type. However, in the BE(2)-Ml7 cell but not the BE(2)-C cell, the same concentrations of dexamethasone added to 30 μM forskolin augmented levels of CRF secretion and content. Likewise, the same augmented response in CRF secretion and content was seen only in the BE(2)-M17 cell line when nanomolar concentrations of dexamethasone were added to 20 nM TPA. Furthermore, only in the BE(2)-M17 cell line were micromolar levels of the biogenic amine serotonin able to increase levels of CRF secretion and content. No effects on CRF in both cell lines were demonstrable with picomolar levels of interleukin-10: as well as micromolar levels of acetylcholine, norepinephrine, arginine-vasopressin, oxytocin, and angiotensin-II. The potential usefulness of these cells as models of central nervous system or placental CRF-containing neurons is discussed.

Notes: Adrenomedullin (ADM) is a 52 amino-acid peptide which is a potent vasodilator in rats, and suppresses basal and CRF-induced ACTH release from cultured pituitary cells. The present study examines the hemodynamic and hormonal actions of human ADM (1–52) infusion in conscious, chronically instrumented sheep. Five sheep were infused intravenously (IV) or intracerebroventricularly (ICV) with ADM at 100 pg/h for 60 min, and mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral conductance (TPC), coronary blood flow (CF), coronary conductance (CC), peak aortic flow (Fmax), and left ventricular dF/dt were monitored by a computer-based data collection system every 2 min. Plasma concentrations of adrenocorticotropin (ACTH), arginine vasopressin (AVP) and renin were measured after 60 min of infusion. IV ADM produced a small fall in MAP of 3 ± 1 mmHg, associated with a reflex increase in HR of 14 ± 3 b/min. CO increased by 1.3 ± 0.3 1/min, whereas SV remained unchanged. TPC was markedly increased by 20 ± 3 ml/min/mmHg. Changes in CF were also seen with an increase of 10 ± 2ml/min, and CC increased in parallel by 0.15 ± 0.02 ml/min/mmHg. Fmax and dF/dt showed small increases of 2.1 ± 0.5 Vmin and 85 ± 20 1/min/sec respectively. Plasma concentrations of ACTH and cortisol were reduced by 58% and 55% respectively, whereas plasma renin concentration increased by 106%. There was no change in plasma levels of AVP. ICV infusion of ADM had no effect on any parameter measured. These data suggest that systemic ADM produces a sustained vasodilator action to lower blood pressure in sheep, and this is the first study to report the ACTH-suppressor action of ADM in conscious animals. ADM may therefore be an important hormone involved in the regulation of pituitary/adrenal function, in addition to its cardiovascular and fluid regulatory actions in mammals.