Preliminary investigations of some derivatives of oxamniquine.

Oxamniquine is a potent schistosomicide used clinically in the treatment of infections due to Schistosoma mansoni. Although relatively well tolerated, some central nervous system (CNS) effects characterised by convulsions have been reported in a small proportion of the population receiving this drug. Oxamniquine, the major metabolite and the secondary alcohol have been screened for convulsant activity by assessing their ability to potentiate catechol induced seizures in urethane anaesthetised mice. Significant (p < 0.05) potentiation was observed with subconvulsive doses (1.5 mg/kg) of strychnine. In contrast, oxamniquine and the secondary alcohol, each at 200 mg/kg ip, both produced significant (p < 0.05) depressions of seizures in this model whereas no effect was seen following 140 mg/kg ip of the acid derivative. These results indicate anticonvulsant rather than convulsant activity in oxamniquine and the alcohol derivative. The failure to observe any effect with the acid derivative may have been due to poorer CNS penetration.

Effects of diabetes on cholinergic transmission in two rat gut preparations.

The gut may be a site of early diabetic neuropathy in humans and rats. The latter may provide appropriate models of these conditions. Therefore, cholinergic function was examined in two gut smooth muscle preparations from control, 30-day, and 6-month streptozotocin-diabetic and similarly diabetic rats that had received continuous treatment with an aldose reductase inhibitor, ponalrestat. Responses of terminal ileum longitudinal muscle to transmural nerve stimulation were depressed in preparations from untreated 30-day diabetic animals. Responses to exogenous acetylcholine were also depressed, by at least the same extent, in preparations from both 30-day and 6-month diabetic groups. Ponalrestat treatment prevented both changes in the 30-day study but did not prevent a depression of responses to acetylcholine in the 6-month study. Neither diabetes nor ponalrestat affected responses of esophageal muscularis mucosa to electrical stimulation or to exogenous acetylcholine. These observations suggest a change in the smooth muscle and/or noncholinergic innervation rather than in the cholinergic nerves of the ileal preparation. Cholinergic function in the ileum did not, therefore, seem to be an appropriate model of diabetic neuropathy.

Tissue noradrenaline and the polyol pathway in experimentally diabetic rats.

1. The effects of a six week period of streptozotocin-induced diabetes on tissue catecholamines and on in vivo noradrenaline turnover were assessed in rats. 2. Noradrenaline concentrations measured in heart ventricle, terminal ileum, vas deferens, spleen and adrenal tissue from the diabetic rats were all found to be elevated compared to those found in control rat tissues. The adrenaline contents of the adrenal glands were also raised in these animals. 3. Noradrenaline turnover in heart ventricle, terminal ileum and vas deferens was estimated from the decline in tissue content of the amine following inhibition of its synthesis with alpha-methyl-p-tyrosine. Turnover was found to be increased in all three tissues. 4. The involvement of the polyol pathway in the above changes was investigated by examining the effects of continuous treatment with an aldose reductase inhibitor, Statil (ICI 128436) or dietary myo-inositol supplementation. Either treatment was found to prevent or reduce the increases in tissue noradrenaline and in its turnover. Myo-inositol treatment also partially prevented the rise in adrenal adrenaline. 5. It is concluded that the elevation of tissue catecholamines and of noradrenaline turnover by diabetes was related to myo-inositol depletion secondary to excessive sorbitol synthesis. Possible mechanisms for the observed increase in noradrenaline turnover could involve Na+, K+-ATPase depression.

A comparison between atria from control and streptozotocin-diabetic rats: the effects of dietary myoinositol.

1. Atria, isolated from control rats, six-week streptozotocin-diabetic rats and from similarly diabetic rats treated with myo-inositol (MI) were compared. The MI treatment was shown to reverse the depressed sciatic nerve MI which was observed in the untreated diabetic group. 2. Spontaneously beating atria from the untreated diabetic animals beat more slowly, and with greater force than tissues from the control group. When electrically driven at 4 Hz they were found to be less sensitive to the negative inotropic effect of acetylcholine. No differences between the two groups were observed in responses to isoprenaline. 3. Intramural nerve stimulation in the presence of 10(-6)M propranolol (vagal stimulation) had a greater negative inotropic effect in the untreated diabetic rat atria than in the controls. Positive inotropic responses to nerve stimulation in the presence of 10(-6) M atropine (sympathetic stimulation) were not significantly different between the two groups. 4. Atria from the MI-treated diabetic animals were found to have a lower spontaneous contractile force and greater sensitivity to acetylcholine than tissues from the untreated diabetic animals. The values obtained in both cases were similar to those from the controls. No significant effect of MI treatment on spontaneous contractile rate or on responses to nerve stimulation was demonstrated. 5. Atrial (mainly myocardial) MI was measured in additional control, six-week diabetic and six-week MI-treated diabetic animals. A significantly higher concentration was observed in the MI supplemented group compared to the untreated diabetic group. The mean MI content in the latter group was lower than that obtained from control tissues but not significantly so. 6. The results implicate MI depletion either in the neurones or in the myocardium in at least some of the changes observed. Possible mechanisms involved are discussed.

Muscarinic receptor density is reduced in diabetic rat atria, an effect prevented by the aldose reductase inhibitor, Statil.

Binding assays using [3H]quinuclidinyl benzilate (QNB) as a muscarinic receptor ligand were carried out on atrial tissue from 6 control and 11 six-week streptozocin-diabetic rats. Five of the latter had received the aldose reductase inhibitor, Statil (25 mg kg-1 day-1 orally). Dissociation constants for specific (atropine displaceable QNB) binding were not changed either by diabetes or Statil treatment. Muscarinic receptor numbers, as estimated by Bmax values, were, however, significantly depressed in tissues from the untreated diabetic group, compared with tissues from either the controls or the Statil-treated diabetic group. These results may explain the reduced sensitivity to muscarinic agonists previously observed in atria from similarly diabetic rats and indicate the involvement of the sorbitol pathway in the change. Possible mechanisms are discussed.

Reversible reduction in bone blood flow in streptozotocin-diabetic rats.

Tibial growth and blood flow were both found to be markedly reduced in anaesthetised streptozotocin-diabetic rats compared to controls. Insulin treatment restored tibial growth to approximately control values and increased tibial blood flow to above control values. The observations are likely to be related to reduced bone turnover in uncontrolled diabetes.

Effects of streptozotocin-induced diabetes and noradrenaline infusion on cardiac output and its regional distribution in pithed rats.

46Sc-and 99mTc-labelled microspheres were used to measure the effects of noradrenaline infusion on cardiac output and its regional distribution in 10 control and 10 streptozotocin-diabetic pithed rats. Plasma noradrenaline concentrations during the infusion were similar in both groups. Pressor responses were significantly smaller in the diabetic animals (controls: + 79, diabetic: + 44 mmHg; p less than 0.001). Cardiac output remained similar in both groups before and during the noradrenaline infusion. Total peripheral resistance was similar in both groups before noradrenaline but the noradrenaline-mediated increase was significantly smaller in the diabetic animals (controls: + 150%, diabetic: + 76%; p less than 0.05). Noradrenaline-mediated resistance increases were significantly reduced in several tissues of the diabetic rats including the small intestine (controls: + 132%, diabetic: -4%; p less than 0.005), the large intestine (controls: + 150%, diabetic: + 39%; p less than 0.05) and the kidneys (controls: + 180%, diabetic: + 27%; p less than 0.05), but were very similar in other areas, e.g. in the hindlimbs and tails.

The role of estrogen and progesterone in the control of preputial gland sex attractant odors in the female rat.

Sexually experienced male rats were used to test the attractiveness of body odors of female rats. The attractiveness of these odors varied with the estrous cycle. Odors from female rats in proestrus were the most attractive to male rats and those from female rats during the darkness hours of diestrus the least attractive. The preputial glands appeared to be the source of these odors for the male rats showed no preference for the odors of proestrous female rats that had been preputialectomized. Administration of 1 microgram estrdiol benzoate (EB) for 5 days increased the attractiveness of body odors of ovariectomized rats. A higher dose of EB (5 microgram) had the same effect when administered for 1 or 5 days although the increase that occurred after 3 days was not significant. A single dose of progesterone (P) (500 microgram) on the other hand, decreased the attractiveness of ovariectomized female odors although no change was seen after 3 days of treatment. A single injection of P also decreased the attractiveness of odors of ovariectomized females that had received EB for 3 days. However, P failed to decrease the attractiveness of odors in ovariectomized females after preputialectomy. We conclude that the preputial glands are an important source of sex attractant odors in the female rat and that the changes in the release of these odors that occur throughout the estrous cycle and pregnancy are controlled by ovarian steroids. While estrogen acts to stimulate the production and release of these odors P appears to inhibit their release.

Variations in plasma concentrations of alpha-melanocyte-stimulating hormone during the oestrous cycle of the rat and after administration of ovarian steroids.

Plasma concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH) were measured by radioimmunoassay at various times during the oestrous cycle of the rat. Variations in plasma alpha-MSH concentrations occurred throughout the oestrous cycle. Plasma alpha-MSH concentrations were low during the day of dioestrus 1 and rose during the evening reaching peak levels at around 02.00 and 06.00 h on dioestrus 2. Plasma alpha-MSH concentrations then fell and remained low throughout the rest of dioestrus 2. A different pattern was observed during pro-oestrus and oestrus. On those days peak alpha-MSH concentrations occurred during the morning and persisted until the onset of the dark period at around 17.00 h. Plasma alpha-MSH concentrations in ovariectomized rats were found to be increased 24 h after administration of a single injection of oestradiol benzoate and at 12 and 36 h after a single injection of progesterone. It is suggested that these ovarian steroids may influence the rhythm in plasma alpha-MSH concentration that occurs during the oestrous cycle.

Comparison between spontaneously beating atria from control and streptozocin-diabetic rats.

Isolated spontaneously beating atria from streptozocin diabetic rats were compared with those from controls. Diabetic atria were found to have reduced rates, increased forces of contraction and reduced sensitivity to the inotropic effects of noradrenaline, isoprenaline, tyramine and calcium. Positive chronotropic responses to tyramine were also reduced but those to noradrenaline and isoprenaline were increased suggesting that tyramine releasable stores of noradrenaline were reduced. Elevation of glucose concentration in the medium from 5.6 to 27 mM resulted in decrease of inotropic sensitivity to the agents used in both control and diabetic rat atria. Resting contractile force of control rat atria was reduced by the inclusion of either 22 mM 2-deoxyglucose, 10(-3) i.u. insulin ml-1 or 5 mM acetate in the medium. The rate was also reduced by medium containing 2-deoxyglucose but increased by insulin. 2-Deoxyglucose also reduced inotropic but increased chronotropic sensitivity to isoprenaline. Possible mechanisms responsible for the changes observed are discussed.

Effects of experimental diabetes and genetic obesity on regional blood flow in the rat.

Blood flow through various tissues of streptozotocin- and alloxan-diabetic and genetically obese rats was compared with that of controls by a radioisotopically labeled microsphere technique. Total cardiac output per unit body weight was unchanged in the diabetic group but decreased in the obese animals. The proportion of cardiac output received by the kidney and organs of the gastrointestinal tract was increased in the diabetic animals. Tissue hyperplasia appeared to be largely responsible. Blood flow per unit weight was markedly increased in the fat tissue of diabetic rats but was reduced in that of the obese rats, indicating a positive relationship between fat mobilization and blood flow. Blood flow in the hindlimbs, tail, skin, and spleen were all reduced in at least one diabetic group. Most of the changes observed appeared to progress with the duration of diabetes. Possible hormonal and metabolic causes are discussed. Some of the experimental changes observed may form useful models for diabetic vasculopathy.

Effect of experimental diabetes, food deprivation and genetic obesity on the sensitivity of pithed rats to autonomic agents.

1 The sensitivities of alloxan and streptozotocin diabetic and hereditary obese pithed rats to acetylcholine, isoprenaline and noradrenaline were compared to those of controls. 2 Blood pressure and heart rate recordings made before dosing was started showed the streptozotocin-treated animals to have a significantly reduced heart rate and increased pulse pressure as compared with controls. 3 Both diabetic groups were found to have reduced sensitivities to the pressor effect of noradrenaline, the depressor effect of acetylcholine, the positive chronotropic and inotropic effect of isoprenaline and the reduction in diastolic pressure induced by isoprenaline. The reduction in sensitivity was generally much greater in the streptozotocin diabetic animals. 4 The genetically obese rats were found to have similar sensitivities to all three agents as did their non-obese litter mates. 5 When either diabetic group was deprived of food for 24 h preceding the tests the sensitivities were found to be raised significantly towards normal in almost all cases. 6 The results are contrasted with previous in vitro results and possible causative metabolic factors discussed. It is suggested that sensitivity changes are unevenly distributed within the cardiovascular system.