Effect of glucagon and glomerulopressin on the renal function of the dog.

Glucagon was infused through the porta or through the left renal artery in dogs. Another group of dogs were infused with glomerulopressin through the left renal artery. It was observed that glucagon when infused through the portal vein enhanced the glomerulopressin production and the glomerular filtration rate (GFR). When glucagon was infused intrarenally it did not alter GRF but it had a direct tubular action decreasing sodium reabsorption in the proximal tubule. Glomerulopressin infused intrarenally increased GRF and potassium excretion. The results suggest that the increase in GFR was due to increase in glomerulopressin activity. There are three reasons for this statement: a) GRF increased when glomerulopressin activity was high, but not when there was a low activity, 5) intrarenally infused glomerulopressin produced a very significant change in the GFR of the infused kidney, while the GRF of the contralateral kidney remained unchanged and c) intrarenally administered glucagon had no effect on GFR.     

Isolated dog coronary arteries response to glomerulopressin

Coronary arteries were excised from pentobarbital anesthetized normal dogs. The isolated coronary arteries were placed in an oxigenated KRB bathing solution maintained at 37 degrees C and pH 7.4 changes in the basal tone were measured. The addition of glomerulopressin to the bathing solution produced a decrease of 26 +/- 1.5 mg of the basal tone. This decrease was prolonged for more than 40 minutes. Several inhibitors of prostaglandins synthesis were added to the bath such as corticosterone (2 X 10(-5) M), indomethacin (6 X 10(-6) M), acetylsalicylic acid (1.8 X 10(-4) M) and tranylcypromine (4 X 10(-4) M). All these inhibitors blocked the action of glomerulopressin. We conclude that glomerulopressin relaxes the coronary arteries and that this relaxation may be mediated through the novobiosynthesis of prostaglandins.     

Inhibition of the stimulatory effect of ACTH on adrenal and ovarian blood flow by indomethacin in the dog.

In anoestrous dogs heated thermocouples were inserted into one of the adrenals and ovaries. The basal adrenal and ovarian blood flow was recorded and enhanced by 1.2, 2.5 or 5.0 micrograms/kg of intravenous ACTH before and after the intravenous administration of 20 or 50 mg/kg of indomethacin. Indomethacin, depending on the dose and on the time elapsing after its administration inhibited the enhancing effect of ACTH on adrenal and ovarian blood flow. Since indomethacin is a specific inhibitor of prostaglandin synthesis it has been suggested that prostaglandins act as mediators in the vasodilatation elicited by ACTH in the canine adrenal and ovary.     

Effect of glucagon on glomerulopressin production in diabetic dogs

Glucagon (21.5 +/- 0.23 ng/min/kg) was infused through the portal vein of normal or pancreatectomized dogs. It was observed that a dose of glucagon that produces no significant change in the glycemia of normal dogs has a very small activity in the production of glomerulopressin and does not alter glomerular filtration rate (GRF). In pancreatectomized dogs this same dose of glucagon also does not alter glycemia but it induces a large increase in the production of glomerulopressin and GFR. Our results suggest that in pancreatectomized dogs glomerulopressin production is more sensitive to glucagon infusion than in normal dogs.     

Enhanced glomerulopressin production and glomerular filtration rate by amino acid infusion in normal humans

Amino acid infusion induces a rise in glomerular filtration rate (GFR) in normal subjects, but the mechanism is as yet unknown. Glomerulopressin infused into the renal arteries of rats and dogs increases GFR. The aim of this study was to ascertain whether amino acid infusion raised glomerulopressin production and GFR. Accordingly, before renal arteriovenography, in 11 potential kidney donors, the caval catheter was introduced into the right hepatic vein and 60-ml blood samples were collected at the beginning and end of each experiment; six patients received amino acid infusion and five a saline infusion. Glomerulopressin in ultrafiltrates from hepatic vein plasma was measured by toad bioassay and GFR determined with diethylenetriamine pentaacetic acid-Tc99. The amino acid-infused group showed significant glomerulopressin activity in ultrafiltrates, as well as a significant GFR increase, whereas in the control group no glomerulopressin activity was observed, and there was no change in GFR. These findings suggest that intravenous amino acid infusion stimulates glomerulopressin production, which may in turn induce an increase in GFR.     

Effects of alfa-receptor and adrenergic neuron blockade on indomethacin-induced changes of renal haemodynamics

The effect of prostaglandin synthesis inhibitor indomethacin was studied on renal haemodynamics by radioactive microspheres in untreated control dogs and in animals treated by the alfa-adrenergic receptor blocking agent phentolamine or by the adrenergic neuron blocking agent guanethidine. RBF was reduced by indomethacin. The reduction of blood flow was more pronounced in the inner cortical zones, which resulted in a blood flow redistribution towards the superficial cortical regions. Urine flow, osmotic concentration and electrolyte excretion did not change significantly. Pretreatment by phentolamine or by guanethidine did not influence the effect of indomethacin on renal haemodynamics or renal function. These data suggest that the sympathetic nervous system is not involved in the renal effects of indomethacin.     

Biphasic effects of platelet-activating factor on coronary blood flow in anesthetized dog

Platelet-activating factor (PAF), modulates vascular tone by influencing prostaglandin release and vascular permeability. To determine its coronary effects we administered RAF (0.3 to 10 ug) into the left main coronary artery of anesthetized dogs with patent left circumflex (LCx) and narrowed left anterior descending (LAD) coronary arteries. RAF produced an initial increase followed by a decrease in coronary blood flow (CBF). The CBF increase was greater in the patent LCx than in the narrowed LAD, but the decrease was similar in both. These effects of RAF on CBF were dose-dependent, and associated with an increase in prostacyclin and thromboxane A₂ metabolites. To examine the contribution of prostaglandin release in coronary effects of PAF, dogs were pretreated with indomethacin (5 mg/kg) followed by administration of PAF. In indomethacin-pretreated animals, the coronary effects of RAF were significantly attenuated. This study shows that RAF has biphasic effects on CBF in the normal coronary artery, but the major effect in the narrowed coronary is decrease in CBF. These effects of RAF can be attenuated by prior treatment of dogs with indomethacin.     

Ethacrynic acid induced release of prostaglandin E to increase renal blood flow

Ethacrynic acid administered to anesthetized dogs was found to increase the level of prostaglandin E as determined by radioimmunoassay in renal venous blood at the time when renal blood flow was increased by this agent. No change was found in the renal venous level of prostaglandin F. When ethacrynic acid was administered after treatment with indomethacin, which blocks the increase in renal blood flow induced by the natriuretic agent, no increase in the renal venous level of prostaglandin E was seen. Thus, the dilation of the renal vasculature would appear to be caused by a stimulation of synthesis and release of prostaglandin E by ethacrynic acid.     

Skeletal muscle vasoconstriction produced by prostaglandin synthesis inhibitors; dependence on pump perfusion

A comparison was made of the effect of prostaglandin synthesis inhibitors (PGSI) on systemic blood pressure and hindlimb muscle vascular resistance of anesthetized dogs under different experimental conditions. When muscle blood flow was monitored using an extracorporeal or noncannulating electromagnetic blood flow probe, indomethacin (5 mg/kg i.v.) increased blood pressure slightly, but did not change vascular resistance. Administration of PGSI (indomethacin, meclofenamate, or naproxen, 5 mg/kg i.v.) after 2 hr of pump perfusion of the hindlimb caused a 22% increase in blood pressure, and 39% increase in vascular resistance 30 min afterwards. When administered immediately after instituting pump perfusion, indomethacin caused no significant change in blood pressure or vascular resistance at the 30 min interval, but at 60 min vascular resistance was increased. A similar vasoconstrictor response to indomethacin was obtained when it was infused in a lower dose intraarterially to the hindlimb, or when given i.v. after ligation of the renal pedicles. The results indicate that pump perfusion results in elaboration of a nonrenal prostaglandin(s) which maintains a vasodilator influence on the skeletal muscle vascular bed.     

The role of alpha-adrenergic receptors in the vasoconstrictor response induced by indomethacin in the kidney.

The effect of indomethacin, an inhibitor of prostaglandin (PG) synthesis, was studied on the renal circulation, Na+ and water excretion in anaesthesized dogs during alpha-receptor inhibition. Indomethacin decreased cortical blood flow (CBFcontr, 454 +/- 142; CBFindo, 332 +/- 51 ml per min per 100 g; p less than 0.02) as well as medullary blood flow (OMBFcontr, 339 +/- 95; OMBFindo, 183 +/- 46 ml per min per 100 g; p less than 0.001), salt and water excretion, further it caused a shift in the intrarenal blood flow distribution toward the cortex. Alpha-blockade prevented the indomethacin-induced vasoconstriction in the cortex (CBF alpha inhibition + indo, 455 +/- 76 ml per min per 100 g) but not in the medullar (OMBF alpha inhibition + indo, 259 +/- 102 ml per min per 100 g, p less than 0.05). Alpha-blockade failed to prevent the indomethacin-induced antidiuresis, antinatriuresis and the intrarenal blood flow redistribution. GFR remained unaffected in all three series of studies. Our experimental findings are in line with the presumption that alpha-receptors are involved in the renal circulatory changes caused by indomethacin, probably as a result of an enhanced NE release during the inhibition of PG production. A NE--PG feed back mechanism is suggested in the regulation of renal circulation. The reduction of salt and water output induced by indomethacin appears to be independent of the alterations in renal haemodynamics, and seems rather to be the result of enhanced Na+ reabsorption, predominantly at the distal segment of the nephron, in the absence of PG, and/or a direct action of indomethacin.     

Effects of indomethacin and prostaglandin F2α on ovulation and ovarian contractility in the rabbit

The present investigation was carried out to determine whether inhibition of ovulation in the rabbit by administration of indomethacin can be correlated with any change in ovarian contractility at ovulation time and can be reversed by administration of prostaglandins. Indomethacin was adminstered intra-muscularly using three different schedules in a dose of 5 mg/kg. A reduced number of ruptured follicles following HCG was noted in all groups treated with indomethacin. Infusion of PGF_2α into the aorta (1 μg/kg/min.) could reverse this effect. Less pronounced ovarian contractility was observed after indomethacin treatment, but infusion of PGF_2α immediately enhanced contractility in ovaries from indomethacin treated rabbits. The inhibition of ovulation in the rabbit associated with indomethacin adminstration may be related to suppression of ovarian contractions. These data also suggest that prostaglandins may play a significant role in the mechanism of ovulation through an influence on ovarian contractility.     

Induction of glomerulopressin production by cyclic AMP

Isolated rat livers were perfused with gassed Krebs-Ringer-Bicarbonate and different doses of theophylline and dibutyryl cyclic AMP were added to the perfusing solution. The perfusates were ultrafiltrated through Diaflo UM-05 membranes. The glomerulopressin activity of the ultrafiltrates were assayed in the tonic tension contraction (TTC) of isolated stomach fundus from rats. As glomerulopressin is known to be a glucuronide, it was inactivated with beta-glucuronidase to confirm that the effect on the stomach fundus was due to the glomerulopressin and not to another substance. It was observed that doses of theophylline between 2 x 10(-3) M and 2 x 10(-5) M enhanced glomerulopressin production. However, there was no relationship between dose of theophylline and the response, and a dose of theophylline 2 x 10(-6) M has no activity. The perfusion with dibutyryl cyclic AMP at 5 x 10(-8) M increased the amount of glomerulopressin produced by the liver. This was a log-dose response of glomerulopressin production to dibutyryl cyclic AMP between 5 x 10(-8) M and 5 x 10(-4) M. Theophylline (2 x 10(-6) M) potentiated the activity of cyclic AMP (5 x 10(-8) M). These results support the view that cyclic AMP is intracellular mediator of the hepatic production of glomerulopressin.     

Prevention of blockage of partially obstructed coronary arteries with prostacyclin correlates with inhibition of platelet aggregation.

Coronary arteries (circumflex or left anterior descending) of anesthetized dogs were partially obstructed to approximately 5% of the normal lumen size by fitting a plastic cylinder around the vessel. Under these conditions, blood flow in the artery was not maintained but, instead, gradually declined over a few minutes until the vessel was completely blocked. Shaking the plastic obstructor restored blood flow temporarily, however, flow gradually declined again to zero. Sometimes flow was spontaneously restored by immediate increases that occurred at irregular intervals while, on other occasions, blood flow had to be restored by shaking the obstructor every time the rate declined to near zero. Intravenous infusion of prostacyclin (PGI2) at 15 to 150 ng/kg/min reversed and prevented the blockage of the coronary arteries. The efficacy of PGI2 in preventing blockage correlated with inhibition of ADP-induced platelet aggregation in platelet rich plasma prepared from blood samples withdrawn from the dogs during PGI2 infusion. Other coronary vasodilators, nitroglycerin and PGE2, that have no antiaggregatory effects, failed to prevent blockage whereas PGE1 and indomethacin, which do block aggregation, also prevented blockage of the vessels. PGI2 or its precursor, PGH2, dripped topically on the obstructed site prevented the blockage of the artery. This local effect of IGI2 could be obtained with amounts too small to cause systemic inhibition of platelet aggregation. The results show that PGI2 prevents blockage of partially obstructed coronary arteries and this effect correlates with inhibition of platelet aggregation. Furthermore, the data suggest that locally produced PGI2 may have a local antiaggregatory effect without inhibiting platelet aggregation in the general circulation.     

Effects of ovarian hormones on ovarian capillary blood flow in anoestrous ewes

The indicator fractionation technique with [86Rb]rubidium chloride as the indicator was used to determine the relative blood flow (RBF) as a measure of capillary blood flow in the ovaries of conscious, hormonally treated, anoestrous ewes. Treatment of ewes with either progesterone only or oestradiol only had no effect on ovarian RBF, but treatment with oestradiol subsequent to progesterone caused a significant increase (P less than 0.001). Consequently, it appears that progesterone-induced sensitivity of the ovarian vasculature to the vasodilatory effects of oestradiol may be responsible for increased ovarian blood flow around oestrus in cyclic ewes.     

Leukotriene D4 reduces coronary blood flow in the anesthetized dog

We studied the effects of intracoronary administration of leukotriene (LT)D4 on coronary blood flow and myocardial function in chloralose anesthetized dogs. For comparison, the effects of injections of U-46619 were examined in the same dogs. Both LTD4 and U-46619 decreased coronary blood flow, left ventricular dP/dt and cardiac output. LTD4 was ten times more potent than U-46619 in decreasing coronary blood flow. The effects of neither drug were different after indomethacin administration.     

Effects of prostaglandins on ovarian blood flow in the bitch

Oestrus and anoestrous mongrel dogs were anaesthetized with chloralose-urethane. In one group, the ovaries were isolated in situ and the effects of a 15-min infusion of PGF-2alpha or PGE-2 on perfusion pressure were measured. In the other group, heated thermocouples were introduced into the stroma of each ovary to measure the changes of local blood flow in response to PGF-2 alpha and PGE-2 infused into the ovarian bursa for 15 min. Intra-arterial infusion of 25.50, 100 or 200 ng PGF-2alpha/kg/min did not affect perfusion pressure; PGE-2 doses of 3.1, 6.2, 12.5 or 25 ng/kg/min caused reductions in proportion to the dose. All doses of PGE-2alpha (50.0, 100 or 200 ng/kg/min) or PGE-2 (25, 50 or 100 ng/kg/min) increased blood flow in the ovarian stroma in proportion to the dose when administered by infusion into the ovarian bursa. There were no differences in the results from oestrous and anoestrous dogs. It is concluded that PGF-2alpha changes intraovarian blood distribution without interfering with the total blood flow while PGE-2 increases both the total and local ovarian blood flow.     

Action of ACTH in the luteal ovary.

Oestrous rats and golden hamsters were anesthetized with pentobarbital, one of the femoral arteries and veins and one of the ovarian veins were cannulated. Blood fractions were collected from the ovary. After the first two fractions synthetic adrenocorticotropic hormone (ACTH) or human chorionic gonadotropin (hCG) was injected i.v. Blood pressures and ovarian blood flow were continuously recorded. Progesterone (P) and oestradiol-17 beta (E2) were determined from the ovarian venous blood by radioimmunoassay (RIA). ACTH induced a temporary elevation in the ovarian blood flow, P and E2 secretion both in rats and hamsters. In rats and hamsters hCG induced a continuous elevation in P secretion but the ovarian blood flow and E2 secretion remained unchanged. Luteal cells from pseudopregnant rats or oestrous hamsters were dispersed with collagenase and incubated with ACTH or hCG. A sample of the cells was preincubated with polymixin-B, indomethacin or ibuprofen. P and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) contents of the medium and cyclic 3,5 adenosine monophosphate (cAMP) content of the cells were determined by RIA. ACTH stimulated the release of 6-keto-PGF1 alpha and the secretion of P from the luteal cells of both species, which was inhibited by indomethacin or ibuprofen, but ACTH did not alter the cAMP content of luteal cells. The polymixin-B prevented ACTH to stimulate P secretion, but it did not elevate the 6-keto-PGF1 alpha release, while the cAMP content of the cells remained unchanged. It is supposed that the polyphosphoinositol-Ca(2+)-protein kinase-C second messenger system is involved in the ACTH induced stimulation of P secretion.     

Effects of indomethacin on local blood flow regulation in canine heart and kidney.

In two series of experiments we studied the effects of indomethacin on (a) coronary reactive hyperemia and, (b) renal blood flow, autoregulation, and reactive dilation. Coronary blood flow was measured in closed-chest dogs. Reactive hyperemia was induced by coronary occlusion for 5 and 15 sec. Indomethacin, an inhibitor of prostaglandin synthesis, was infused intra-arterially in doses of 90-200 mg over periods ranging from 30-120 min. Coronary reactive hyperemia was not affected by indomethacin. The canine renal vascular bed was studied under conditions of natural flow, controlled flow, and controlled pressure. Intra-arterial infusion of 90 mg of indomethacin over a 30- to 60- min period caused increased renal vascular resistance and an attenuation of reactive dilation (induced by stopping renal blood flow for 90 sec). Indomethacin slightly attenuated the autoregulatory response to decreasing perfusion pressures, but did not affect the respone to increasing pressures. Thus the study fails to provide evidence for participation of the prostaglandins in regulation of coronary blood flow and suggests only minimal participation of prostaglandings in renal blood flow regulation.     

The effect of inhibition of prostaglandin synthesis on ovarian hypertrophy in the rat.

Aspirin and indomethacin, inhibitors of prostaglandin biosynthesis, were utilized to determine the role of prostaglandins (PGs) in ovarian weight gain in rats following unilateral ovariectomy or treatment with PMSG. After unilateral ovariectomy, the compensatory ovarian hypertrophy was 185-0% compared with 139-8% and 97-5% in rats treated with indomethacin and aspirin, respectively. The adrenal weights in rats treated with aspirin were also reduced significantly. Administration of PGE2 or PGF2alpha with aspirin reversed the effect of aspirin on the adrenals but had no effect on the ovarian weight. Indomethacin and aspirin treatment of animals injected with PMSG also reduced the ovarian weight gain. If 100 mug PGE2 were given twice daily, this effect was reversed in both groups but thrice daily administration had no effect on rats receiving aspirin. In PMSG-treated rats, 100 mug PGF2alpha twice daily did not reverse the effect of indomethacin and aspirin, and actually enhanced the effect of aspirin.