Vasoactive intestinal polypeptide regulation of rabbit renal adenylate cyclase activity in vitro

1. The effect of vasoactive intestinal polypeptide (VIP) upon adenylate cyclase activity was determined in purified cortical basolateral membranes and in glomeruli and tubular elements obtained from rabbit kidney. 2. In purified basolateral membranes prepared from cortex, 1 microM-VIP consistently stimulated adenylate cyclase activity above basal levels (1.55 +/- 0.09-fold (mean +/- S.E. of mean), n = 10 animals). Half-maximal stimulation was observed at 17 +/- 11 nM-VIP (S.D., n = 9). 3. Related peptides, e.g. secretin, glucagon, gastric inhibitory peptide, human pancreatic growth hormone releasing factor, and peptide having N-terminal histidine and C-terminal isoleucine amide (PHI), were without effect or gave lower stimulations of adenylate cyclase activity when tested at 1 microM. 4. Significant VIP degradation was observed under the assay conditions used but this did not substantially alter the response or selectivity to VIP. 5. In separate preparations of isolated glomeruli and proximal tubules addition of 1 microM-VIP resulted in a 3.3 +/- 1.1-fold (S.D., n = 3) and 2.2 +/- 1.0-fold (S.D., n = 3) stimulation (respectively) of adenylate cyclase activity. 6. In isolated medullary tubule suspensions, isolated by collagenase-hyaluronidase digestion of outer (red) medulla, and in thick ascending-limb-enriched preparations prepared by Percoll density gradient fractionation, 1 microM-VIP significantly increased adenylate cyclase activity by 2.4 +/- 0.6-fold (S.D., n = 3) and 2.1 +/- 0.7-fold (S.D., n = 3) respectively. 7. A possible role for VIP in the regulation of renal function in the rabbit is discussed in relation to the occurrence of VIP stimulation of adenylate cyclase activity in several renal cellular elements.

The influence of digoxin antibodies on digoxin disposition and effect: studies in guinea-pigs and HeLa cells

Pretreatment of guinea-pigs with digoxin-specific Fab (fragment antigen binding) fragments reduced the cardiotoxicity of intravenously infused digoxin (the lethal doses in Fab-treated and control animals were 1.0 and 0.6 mgkg-1, respectively). At death the serum digoxin concentration was elevated 2 fold in the Fab-treated animals, while the tissue concentrations were generally lower. The 30-40% lower cardiac digoxin concentration (seen in whole homogenate and throughout the subcellular fractions examined) was surprising; presumably this reflects a difference from the controls in the proportion of pharmacologically active/inactive digoxin in this organ. Adding digoxin-specific immunoglobulin G or the Fab fragments to HeLa cells before incubation with digoxin, reduced specific digoxin binding (Na pump-bound) slightly more than the non-specific binding. Adding specific antibody after digoxin, however, did not reduce digoxin binding or effect a recovery in Na pump activity. It seems that the protective effect of digoxin-specific antibodies seen in the guinea-pig can to some extent be simulated using HeLa cells. However, this is apparently not so regarding the widely-reported ability of these antibodies to reverse the action of digoxin.

The serum pharmacokinetics of digoxin as an immunogen and hapten in the rabbit

3H-digoxin was given intradermally 4 weeks before, and at 6 and 44 weeks after immunisation with a 3H-digoxin-human serum albumin conjugate. Before immunisation, the serum digoxin distribution and elimination half-life (t1/2) values were 4.2 h and 2.1 days respectively. The immunogen-associated radioactivity showed characteristic fluctuations during a prolonged distribution phase of about 5 days, but the t1/2 of 2.7 days was similar to that of digoxin, indicating that appreciable cleavage of digoxin from the albumin may have occurred during the distribution period. At 6 weeks after immunisation, following hapten injection there was again a prolonged distribution phase of about 5 days during which concentration of digoxin were some five-fold higher than corresponding pre-immunisation values. The serum elimination t1/2 was 4.1 days. At 44 weeks the differences were even more marked; the distribution phase was some 7 days, during which serum hapten concentrations were approximately ten-fold higher than pre-immunisation values. The serum elimination t1/2 was in this case about 25 days. Surprisingly digoxin-specific antibody titres at 6 and 44 weeks were not significantly different, indicating that measurement of titre, which is a function of both antibody concentration and affinity, is not in itself reliable in predicting changes in hapten pharmacokinetics.

The effect of immunization with digoxin-specific antibodies on digoxin disposition in the mouse

After intravenous dosing, digoxin was rapidly distributed to tissues, with a distribution half-life of 3.0 min. The highest digoxin concentrations at 1 hr post dosing were found in lymph nodes, adrenals, gallbladder (including contents), liver and kidney respectively. Digoxin concentrations in the heart, spleen, brain, lung, skeletal muscle and fat were similar to, or lower than, those in the plasma. The apparent volume of distribution (AVd) was 1 l/kg, and the plasma elimination half-life and clearance (Cl) 2.8 hr and 0.25 l/kg per hr respectively. When digoxin was given one day after passive immunization with digoxin-specific immunoglobulin G (IgG) or Fab fragments the respective plasma digoxin concentrations were elevated some 26- and 5-fold respectively compared with control values. Consequently there were reductions in AVd (93 and 32%) and Cl (94 and 50%). The effect of IgG treatment on clearance was still apparent when the hapten was given up to 14 days after immunization, while the weaker effect of Fab-treatment was less persistent. Although tissue digoxin concentrations were slightly lower in the immunised mice, it was only in the lymph nodes at 10 and 14 days after IgG treatment that the reduction in hapten concentration was statistically significant.

Biochemical and physiological adaptation to chronic propranolol treatment in the rat

The biochemical and physiological aspects of isoprenaline sensitivity in normotensive rats were examined during and after abrupt withdrawal of chronic propranolol treatment. Serum propranolol concentrations in rats chronically treated for one month (0.125% propranolol in drinking water: 75-100 mg/kg/day) ranged from 7 to 23 ng/ml. At the height of the blockade, rats showed a decreased responsiveness in vivo to isoprenaline-induced increase in heart rate and fall in blood pressure; the ED50 values for isoprenaline being increased some 20- and 4-fold respectively. There was a 180% increase in beta-receptor number in sarcolemmal membranes isolated from ventricular muscle of these animals, together with increased basal (290%), fluoride- (100%), forskolin- (80%) and isoprenaline-stimulated (125%) adenylate cyclase activity. Twenty-four hours after propranolol withdrawal, serum propranolol concentrations were reduced by over 95%. At this time rats exhibited increased chronotropic and blood pressure responses to i.v. isoprenaline, indicated by the reduced ED50 values (2-fold and 12-fold respectively compared to controls). In addition, cardiac sarcolemmal beta-receptor number and adenylate cyclase activities were still significantly elevated above those of controls; 35% increase in beta-receptor number and increases of 96, 26, 13 and 37% in basal, fluoride-, forskolin- and isoprenaline-stimulated adenylate cyclase activities respectively. Forty-eight hours after drug withdrawal serum propranolol concentrations were only just detectable at 0.5 +/- 0.1 ng/ml. Although sarcolemmal beta-receptor numbers were still elevated (23%) isoprenaline-stimulated adenylate cyclase activity had returned to control values. However, both the fluoride- and forskolin-stimulated enzyme activities were decreased below control values by 12 and 23% respectively, suggestive of a reduction in the catalytic capacity of the adenylate cyclase complex. In parallel with the reduction in beta-receptor number and adenylate cyclase activity, the chronotropic response to i.v. isoprenaline had also returned to control values. In contrast, the blood pressure response to i.v. isoprenaline was still elevated in these animals indicated by the 5-fold reduction in the ED50 value compared with control animals.

The identification of the goitrogen (-)5-vinyloxazolidine-2-thione (goitrin), as a bitter principle of cooked brussels sprouts (Brassica oleracea L. var. gemmifera)

(-)5-Vinyloxazolidine-2-thione (goitrin), a well-known goitrogen, has been identified as a bitter principle in cooked Brussels sprouts (Br. oleracea var. L. gemmifera). The identification was carried out by chemical analysis and sensory assessment.

Trimethylamine and egg taint

1. The sensory qualities of "crabby", "fishy" tainted eggs are closely similar to those of an aqueous solution of trimethylamine (1 x 10(-2) microgram/g). 2. The odour threshold of trimethylamine in water is 5 +/- 1 x 10(-4) microgram/g. 3. The taint occurs in eggs which contain more than 0.8 microgram/g trimethylamine. The reasons why this concentration is higher than that in water are discussed.

Quantitative selenium metabolism in normal New Zealand women

1. Quantitative selenium metabolism has been studied in normal young New Zealand women by measuring total Se intake and urinary and faecal Se output, and by using values for absorption, excretion and turnover of 75Se determined after administration of[75Se]selenomethionine or [75Se]selenite. 2. In a period of 14 d when a normal ad lib. diet was being consumed, mean dietary Se for four women was 24.2 microgram/d, mean urinary Se was 13.1 microgram/d and mean faecal Se was 10.8 microgram/d; mean Se balance during this time was + 0.3 microgram/d. 3. Intestinal absorption of food Se was 0.76--0.83 of intake (mean 0.79). 4. Whole-body Se was calculated in three different ways; (a) using the specific activity of urinary Se and retained whole-body 75Se; (b) using plasma Se and the occupancy of 75Se in whole-body and plasma; (c) using absorbed food Se and the occupancy of absorbed 75Se in whole-body. 5. Whole-body Se calculated from measurements obtained following the administration of [75Se]selenomethionine was 4.7--10.0 mg (mean 6.9) using method (a), 4.1--7.2 mg (mean 5.2) using method (b) and 4.3--8.9 mg (mean 6.2) using method (c). 6. Whole-body Se calculated from results obtained after giving [75Se]selenite was 2.7--3.4 mg (mean 2.9) using method (a), 2.3--5.0 mg (mean 3.5) using method (b) and 2.1--3.0 mg (mean 2.6) using method (c). 7. The results of this study indicate that the minimum dietary requirement of Se for the maintenance of normal human health is probably not more than 20 microgram/d.

The metabolism of [75Se]selenomethionine in four women

1. The long-term fate of an oral dose [75Se]selenomethionine was studied in four women. 2. Urinary and faecal excretion, respiratory losses and whole-body retention of 75Se were measured, and also 75Se turnover in whole body, plasma and erythrocyte during a period of 33-34 weeks. 3. Intestinal absorption of [75Se]selenomethionine by the four subjects was 95.5-97.3% of the administered dose. 4. Urinary excretion accounted for 6-9% of absorbed 75Se in the first 2 weeks. No radioactivity was detected in expired air.