Library

Notes: Specific, homologous porcine neurophysin I and II radioimmunoassays were established together with specific oxytocin and vasopressin radioimmunoassays. The levels of each of these proteins and peptides were measured in acid extracts of individual paraventricular nuclei, supraoptic nuclei, neurohypophyseal stalks and posterior pituitary lobes of 12 pigs in order to quantitate the neurophysin-hormone relationships in the porcine neurohypophyseal system. Neurophysin III was found to be immunologically identical to neurophysin I. Neurophysin measurements by radioimmunoassay were quantitatively validated by scanning densitometry of polyacrylamide gels stained with 0.5% amido schwarz.In the hypothalamic nuclei vasopressin was in 3–4 M excess of oxytocin but in the neurohypophyseal stalk and posterior pituitary lobe the hormones were equimolar suggesting that the rate of formation of vasopressin differs from that of oxytocin. Neurophysin I immunoreactivity was present in a 3:1 molar ratio with neurophysin II throughout the porcine neurohypophyseal system. In posterior pituitary lobes total neurophysins were equimolar to total hormone concentrations. The specific activity (pmol/mg extracted protein) of oxytocin increased 1800 times, vasopressin 560 times and neurophysins about 360 times from the paraventricular nucleus to the posterior pituitary lobe. In the hypothalamic nuclei relationships between immunoreactive neurophysin I and vasopressin, and between neurophysin II and oxytocin were highly significant. In the posterior pituitary lobe each immunoreactive neurophysin level correlated with both hormone levels. Quantification of densitometric scans of stained polyacrylamide gels from neurophypophyseal extracts and immunoreactivity patterns of neurophysins in eluates of sliced, duplicate gels indicated that neurophysin III decreased distally within the neurohypophyseal tract while neurophysin I increased. The results demonstrated that vasopressin was associated with porcine neurophysin I. However, oxytocin may be associated with both immunoreactive neurophysin I and neurophysin II in the porcine neurohypophyseal system if a 1:1 molar ratio of neurophysin to hormone is to be maintained. Neurophysin III contributed to the stoichiometry of this relationship.

Notes: 1. The rate of clearance of 125I-labelled porcine neurophysins I and II from the circulation of the rat has an initial fast component followed by a slower component.2. In the initial phase of clearance the half-life of neurophysin I was 1·50 min (s.e.m. = 0%%03) and for neurophysin II was 1·74 min (s.e.m. = 0·05). In the slower phase of clearance the half-life of neurophysin I was 22·6 min (s.e.m. = 2·2) and for neurophysin II was 27·3 min (s.e.m. = 5·8).3. The first component had a volume of distribution similar to the blood volume and the second component had a volume of distribution similar to the volume of extracellular fluid of the rat.4. The metabolic clearance rates per 200 g of body weight were 1·94 ml/min (s.e.m. = 0·12) for neurophysin I and 1·29 ml/min (s.e.m. = 0·15) for neurophysin II.5. Using whole-body autoradiography, the kidney was shown to be the major site of uptake of radioactivity in both virgin female and lactating mice.

Notes: 1. Chronic heart failure was induced in rats by ligation of the left coronary artery to produce a left ventricular myocardial infarct.2. Cardiac angiotensin-converting enzyme (ACE) was estimated by radioligand binding in myocardial homogenates and by autoradiography studies of radioligand binding to ACE in heart sections.3. Radioligand binding studies demonstrated an increase in binding sites in animals with myocardial infarction, compared with sham operated animals. Mean increases were 457% in right atrium, 295% in left atrium, 326% in right ventricle, 187% in left ventricle and 530% in the region of the left ventricular infarct, compared with the sham left ventricle.4. Autoradiography studies confirmed tissue homogenate binding studies, demonstrating (i) a marked increase in ligand binding in the infarct area and (ii) an increase in binding density in the hypertrophied myocardium of right and left atrium, and right and left ventricle.5. The induction of cardiac ACE in the myocardium of rats with chronic heart failure may participate in the pathophysiology of cardiac hypertrophy.

Notes: 1. Anaesthetized male Sprague-Dawley rats underwent unilateral nodose ganglionectomy or sham operation.2. One week later hindbrain V1 vasopressin binding site density was assessed by in vitro autoradiography with the selective V1 antagonist radiolgand [125I] [d(CH2)5, Sar7]AVP.3. Specific binding was observed in the nodose ganglion, nucleus tractus solitarius (NTS), area postrema, and inferior olive. Only binding in the medial subnucleus of the NTS was reduced by ipsilateral nodose ganglionectomy.4. These findings are consistent with V1 vasopressin receptors occurring pre-synaptically on vagal primary viscerosensory afferent fibres.5. Such receptors may be involved in the effect of AVP on blood pressure and/or the baroreflex.

Notes: 1. 125I-351A, a tyrosyl derivative of the angiotensin converting enzyme (ACE) inhibitor lisinopril, was used as a radioligand, and radioinhibitor binding and displacement assays have been established.2. The in vitro potency of a range of ACE inhibitors against rat ACE was determined using the radioinhibitor binding displacement assay.3. The concentration of an ACE inhibitor needed to displace 50% of 125I-351A bound to rat ACE (ID50) was closely correlated with the concentration needed to inhibit 50% of ACE enzymatic activity (IC50).4. Radioinhibitor binding displacement assay was used to measure the plasma concentrations of lisinopril, cilazapril and perindopril in rat plasma5. Plasma concentrations of lisinopril measured by radioimmunoassay were identical with that measured by radioinhibitor binding assays.

Notes: 1. Receptor-stimulated hydrolysis of inositol phospholipids was studied in atrial and ventricular myocytes isolated from guinea-pigs.2. Acetylcholine and carbachol stimulated inositol phosphate accumulation with a maximum of more than 12 times the unstimulated values in atrial myocytes and 7 times in ventricular myocytes.3. The vasoactive peptides angiotensin II and vasopressin also stimulated inositol phosphate accumulation, but the maximum effect was lower than that mediated through muscarinic receptors.4. However, the adenosine analogues, l-N6-phenylisopropyladenosine and 5'N-ethylcarboxamidoadenosine which, like muscarinic agonists depress cardiac contractility, did not affect inositol phosphate accumulation at concentrations up to 10−4 mol/1.5. Stimulation of phosphatidylinositol turnover in heart bears no obvious relationship to either contractility or release of atrial natriuretic factor.

Notes: 1 Adenosine analogues N6-phenylisopropyladenosine and 5′-N-ethylcarbox-amidoadenosine inhibit cardiac adenylate cyclase in a concentration dependent manner.2 Inhibition of adenylate cyclase required the presence of guanosine-triphosphate and Mg2+ ion. The concentration of Na+ ion was critically important: maximal inhibition was observed at 50 mmol/1 Na+.3 8-Phenyltheophylline and isobutylmethylxanthine antagonized the inhibition of adenylate cyclase mediated by adenosine analogues.4. Adenosine receptors of the inhibitory type (R1 or A1) are present in guinea-pig myocardium and may mediate some actions of adenosine.

Notes: 1. Administration of captopril (1.5mg/kg i.v.) to anaesthetized dogs was associated with an increase in renal blood flow of 56 ml min-1 (s.e.m. = 13, n= 9) despite a significant fall of 17 mmHg (s.e.m. = 5, n= 9) in mean arterial pressure.2. Treatment of dogs with the angiotensin receptor antagonist, Sar'lle8-angiotensin II (2.5 fxgjkg per min i.v.), or the cyclo-oxygenase inhibitor indo-methacin (10 mg/kg i.v.) did not prevent the renal vasodilation and hypotension following angiotensin-converting enzyme inhibition. This suggests that these effects are neither solely due to inhibition of the renin-angiotensin system nor mediated by prostaglandins.3. Increased urinary kinin excretion, possibly reflecting increased renal concentrations of kinins, accompanied the renal vasodilation after both captopril and renal artery occlusion.4. The kallikrein-kinin system may play a role in the regulation of the renal vasculature in anaesthetized dogs.

Notes: 1. Bradykinin infusion (0.1 μg/min i.v.) decreased the number of uterine bradykinin receptors by 20% at Day 2. Bradykinin receptors returned to control levels at Day 7.2. Captopril infusion (1.7μg/min i.v.) induced prolonged decreases in the number of uterine bradykinin receptors of 15% at Day 2 and of 13% at Day 7, respectively.3. The number of uterine bradykinin receptors was increased in two-kidney, one clip hypertensive rats by 19%.4. These results suggest that endogenous bradykinin participates in the regulation of uterine bradykinin receptors.5. Decreased uterine bradykinin receptors induced by captopril might reflect increased endogenous bradykinin.