Kenneth A. Munday

The half-lives of angiotensin II, angiotensin II-amide, angiotensin III, Sar1-Ala8-angiotensin II and renin in the circulatory system of the rat.

1. Methods are described for estimating the half‐life of angiotensin analogues and renin in the rat, from the time course of the blood pressure changes they evoke. 2. The following half‐life values were measured: angiotensin II, 16 +/‐ 1 sec; angiotensin III, 14 +/‐ 1 sec; angiotensin II‐amide, 15 +/‐ 1 sec; Sar1‐Ala8‐angiotensin II, 6.4 +/‐ 0.6 min; renin, 3.0 +/‐ 0.4 min. The distribution volume of angiotensin was found to be 18 ml./kg body wt. 3. It is inferred that the Asp1 residue does not reduce the rate of angiotensin II catabolism, but that substitution of this residue by sarcosine may inhibit catabolism while substitution by asparagine has no effect. 4. Five experimental criteria were identified which indicate that these methods give reliable estimates of the half‐life. It is suggested that these results are more accurate than most previous half‐life estimates. 5 When tachyphylaxis to angiotensin II‐amide occurs, the pressor activity of the plasma is not reduced.

Effects of angiotensin II on fluid transport, transmural potential difference and blood flow by rat jejunum in vivo.

A method has been described for the measurement of fluid transport by rat jejunum in vivo over two consecutive 30 min periods. 2. Subpressor infusion rates of angiotensin (0‐59 ng/kg per minute) stimulate fluid transport, while high (pressor) infusion rates (590 ng/kg per minute) inhibit fluid absorption. 3. Both the inhibitory and stimulatory effects of angiotensin on fluid transport are not accompanied by any change in the transmural p.d., total blood flow to the jejunum or distribution of blood flow within the wall of the jejunum. 4. These results are discussed in relation to the mechanism of action of angiotensin on fluid transport and its role in sodium and water homoeostasis.

The effect of angiotensin on cation transport by rat kidney cortex slices.

1. A study has been made of the effect of angiotensin (10−12 g/ml.) on active and passive transport of sodium, potassium and water between rat kidney cortex slices and the incubation medium.

Carbohydrate metabolism in Carcinus maenas gill tissue

Abstract 1. 1. Activities of fourteen enzymes of the glycolytic, gluconeogenic and pentose phosphate pathways were measured in extracts of Carcinus maenas gill tissue. 2. 2. Lactate and α-glycerophosphate dehydrogenases had similar activities in gill extract, in contrast to mammals and insects. 3. 3. Estimation of the pyridine nucleotides showed that the total NADP(H) concentration was greater than that of NAD(H). 4. 4. Studies with 1-14C and 6-14C glucose in the presence and absence of arsenite suggest that the major portion of the C6 carbon is liberated via the citric acid cycle. 5. 5. Gill tissue was shown to have a gluconeogenic capacity. The most rapid production of glucose was observed in 50 per cent sea water when 25 per cent of the NaCl content was omitted. Under these conditions with animals collected in the winter months, November to March, and allowing for a Q 10 of two the rates observed in gill were comparable with those obtained using rat liver slices, but were much less during the summer months.

Identification of selective, high affinity [125I]‐angiotensin and [125I]‐bradykinin binding sites in rat intestinal epithelia

1 Specific [125I]‐angiotensin II (AII) and [125I]‐bradykinin (Bk) binding sites have been identified within epithelial membranes from rat jejunum and descending colon. 2 These high affinity intestinal sites exhibited KD values of 0.64 ± 0.16 nM for [125I]‐AII and 0.69 ± 0.13 nM for [125I]‐Bk, which were similar to those for [125I]‐AII (0.85 nM) and [125I]‐Bk binding sites (1.03 nM) previously identified in renal cortex epithelia. 3 Specific [125I]‐AII binding capacity was only 19.77 ± 2.74 fmol mg−1 in small intestine and 11.31 ± 2.66 fmol mg−1 in descending colon epithelia while a larger population, 332.0 ± 72.9fmol‐mg−1 of specific [125I]‐Bk sites were identified in epithelial membranes from small intestine. 4 Significant hydrolysis of both free [125I]‐AII and [125I]‐Bk was observed while membrane bound peptides remained relatively resistant to degradation. Whilst no corrections have been made to the observed values of KD and Bmax quoted above, one may assume that the calculated reductions in the free hormone concentration will result in a decrease of the KD value for both peptides. Loss of membrane bound peptide, particularly of [125I]‐AII, may indicate that the calculated Bmax value is an underestimation. 5 Despite the rapid degradation of unbound [125I]‐AII and [125I]‐Bk during incubations the kinetics of specific peptide binding were reversible and highly selective. The order of potency for specific [125I]‐AII binding was [Sar1, Leu8]‐AII > [Sar1, Thr8]‐AII > AII > [Sar1, Ile8]‐AII > [Des, Asp1, Ile8] AII > AIII. Specific [125I]‐Bk binding was also highly selective, the order of potency being Phe8‐Bk>Tyr8‐Bk>Lys‐Bk>Des, Arg1‐Bk. AII exhibited an IC50 of > ImM for specific [125I]‐Bk binding and likewise Phe8‐Bk for specific [125I]‐AII binding.

The effect of angiotensin II upon electrogenic ion transport in rat intestinal epithelia

1 Epithelial sheets from rat jejunum and descending colon have been shown to respond to angiotensin II (AII) when studied under short‐circuit conditions and bathed on both sides with Krebs‐Henseleit solution. 2 The octapeptide AII elicited increases in short‐circuit current (SCC) in preparations of jejunum and decreases in SCC in the descending colon; both responses occurred when the peptide was applied to the basolateral surface, but not when applied to the apical solution. 3 Responses in both tissues were highly specific, being inhibited by a range of AII antagonists with the following order of potency: [Sar1. Thr8]‐AIi>[Sar1. Leu8]‐AIi>[Sar1. Ile8]‐AIi>[Sar1. Ala8]‐AIi>[Des, Asp1. Ile8]‐AII in rat jejunum. AII responses were not affected by α‐or β‐adrenoceptor antagonists, atropine or tetrodotoxin. 4 AII responses were totally inhibited by the chloride channel blocker, diphenylamine‐2‐carboxylate (DPC) while cotransport inhibitors e.g. piretanide and frusemide significantly reduced the size of AII responses in colon and jejunum. These patterns of activity suggest that in the jejunum the responses result from electrogenic chloride secretion. Although AII responses in colon were sensitive to DPC the transporting ions have not yet been identified. 5 Both piroxicam and indomethacin inhibited the increase in SCC elicited by AII in the jejunum, and the reduction in SCC caused by AII in the colon. Taken together these results indicate that eicosanoids are involved in AII responses in both tissues. 6 This is the first study to demonstrate a direct, electrogenic effect for AII on transporting epithelia from the gastrointestinal tract. The responses are most probably initiated by AII interacting with previously identified specific AII receptors within the epithelial membranes.

The effect of neuroleptic drugs on drinking induced by central administration of angiotensin or carbachol.

The effect of a series of neuroleptic drugs on the drinking response elicited by intracerebroventricular injection of either angiotensin or carbachol into conscious rats was studied. The i. p. injection of haloperidol, cis-flupenthixol, or fluphenazine antagonized both angiotensin-induced and carbachol-induced drinking. When injected into the lateral ventricles, the neuroleptics haloperidol, fluphenazine, cis-flupenthixol and sulpiride were potent inhibitors of angiotensin-induced drinking, but had little effect on the dipsogenic action of carbachol. Clozapine, administered centrally, antagonized drinking caused by both angiotensin and carbachol. Pimozide and chlorpromazine were also potent inhibitors of angiotensin-induced drinking, while trans-flupenthixol was inactive. Our results support the concept of an involvement of dopamine in angiotensin-induced drinking.

Noradrenaline as a possible mediator of the actions of angiotensin on fluid transport by rat rejunum in vivo

1. Net fluid absorption and transmural potential difference were measured in the rat jejunum in vivo.

Studies on the mechanism of action of angiotensin on ion transport by kidney cortex slices

1. A study has been made of the effects of cyclic AMP, phosphodiesterase inhibitors and protein synthesis inhibitors on the response of rat kidney cortex slices to physiological doses of angiotensin.

The effect of salinity on the metabolism of nitrogen-containing compounds by Carcinus maenas

Abstract 1. 1. The level of the ninhydrin positive substances in the tissues of Carcinus maenas changed with both environmental salinity and nutritional status. 2. 2. In 40 per cent sea-water compared with 100 per cent sea-water there is an increased rate of utilization of glutamic acid, both in vivo following injection of U-14C-glutamate and in vitro after its exogenous addition. 3. 3. Glutamine synthesis decreased and U8 production accelerated at the lower salinity from both exogenously added glutamate and endogenously generated glutamate (formed from 2-14C-sodium acetate). 4. 4. Small increases in U-14C-alanine and U-14C-glycine utilization in vitro were observed when the salinity was reduced from 100 to 40 per cent sea-water. 5. 5. Aminotransferase enzymes were not activated by NaCl.