The hippocampal vasopressin receptors have been characterised by measuring the stimulated accumulation of inositol monophosphate in the presence of 10 mM LiCl after hippocampal slices were prelabelled with [3H]inositol. Arginine-vasopressin caused a dose-dependent increase in inositol monophosphate accumulation (ED50 = 7.1 nM). The response was unchanged in the absence of Ca2+ and significantly reduced in the presence of a V1-receptor antagonist. Equimolar oxytocin was ineffective as a stimulus. This suggests that the hippocampal receptors are of the V1 type.

Serum calcium was measured under different circumstances of thyroid dysfunction in male Sprague-Dawley and female Wistar rats. After induction of hypothyroidism with 131I and propylthiouracil, serum calcium fell from a control value of 2.43 +/- 0.08 mmol/l to 2.07 +/- 0.08 mmol/l (P less than 0.01). Thyroid hormone replacement therapy in hypothyroid rats caused a return of serum calcium to control values (2.09 +/- 0.04 mmol/l to 2.41 +/- 0.02 mmol/l, P less than 0.01). Treatment of normal rats with thyroid hormones caused elevation of serum calcium to 2.59 +/- 0.04 mmol/l compared with a control value of 2.44 +/- 0.02 mmol/l (P less than 0.01). Time-course studies demonstrated a slow decline in serum calcium levels over a 10 week period during induction of hypothyroidism with propylthiouracil alone but a very rapid normalization of serum calcium (within 1 h) after replacement therapy with L-tri-iodothyronine. These data illustrate the considerable influence that thyroid hormones exert on calcium metabolism and demonstrate for the first time consistent changes in serum calcium in the rat with hypo- and hyper-thyroidism.

Responses to carbachol, histamine and the sodium-channel agent veratrin were reduced by carbamazepine whilst the responses to 5-hydroxytryptamine, noradrenaline and substance P were unaffected. 5 Inhibition of carbachol, histamine and veratrin-induced stimulation by carbamazepine share a similar dependence on length of pre-incubation time with the drug. However, the effect of carbamazepine (100pM) on the respective dose-response curves suggests that the mechanism of inhibition of the carbachol response differs from the inhibition of the histamine and veratrin responses. These effects may be significant in the mechanism of action of carbamazepine as an anticonvulsant and in its effectiveness against manic depression.

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