Sensitivity of the developing chick myocardium to the positive inotropic effects of calcium and isoproterenol

Summary The present results show that the sensitivity of the chick myocardium to the positive motropic effect of Ca⁺⁺ decreases during development and that the Ca⁺⁺ concentration of the physiological solution used must be lowered below normal to study the effects of positive inotropic agents in preparations from younger embryos. Isoproterenol elicits positive inotropic responses in 7–9-day embryonic ventricle and in newborn chick atria; however, the 4-day embryonic myocardium is unresponsive to isoproterenol.This work was supported by Grant No. HL-15995 from the National Heart Institute (USPHS).The authors would like to thank Dr.F. E. Shideman for the isolated tissue baths used in these experiments.     

Effect of dibutyryl cAMP and theophylline on cultured rat embryonic shields

Summary Effects of N⁶, O² dibutyryl adenosine 3,5-cyclic monophosphate (db-cAMP) and theophylline (Th) on cultured rat embryonic shields were studied. After addition of db-cAMP to the culture medium, an increase of the weight of explants and of the incidence of the skeletal muscle was observed. Theophylline seems to be ineffective.     

The effect of dehydration on the neurohypophyseal blood flow in rats with hereditary diabetes insipidus

Summary Neurohypophyseal blood flow increases in water-deprived rats. This increase is independent of vasopressin release, since it occurs even in rats with hereditary defect of hypothalamic vasopressin synthesis.Acknowledgment. The technical assistance of D. Vilimovská is acknowledged.     

Changes in ecdysone levels in the spiderPisaura mirabilis nymphs (Araneae,Pisauridae)

Summary RIA of ecdysones are made on nymphal extracts ofPisaura mirabilis during the intermoulting cycle. The hormone level is low during exuviation and the greatest part of the intermoulting period but increases notably before and after ecdysis. The main hormonal peak or pre-ecdysial peak is due to -ecdysone, characterized by combined TLC/RIA.Acknowledgment. We wish to thank Dr M. Hirn for his help during the manipulations and J. Britton who has translated the text into English.     

Model of the effect of 4-aminopyridine at the level of potassium channels of the giant axon of the squid, Logigo forbesi L.]

Most of the effects of 4-aminopyridine on the potassium conductance of the giant axon of the Squid can be explained in terms of a simple model based on the physicochemical properties of the molecule and what is known about the structure of the potassium "channels".     

An electrophoretic investigation of the binding of 3-14C coumarin to rat serum proteins

Summary The binding of coumarin to serum proteins of the rat has been demonstrated. Of the total bound coumarin (37% of injected dose), 36% was bound to the slow and fast ₁ globulins, 11% to the post albumins, 10% to globulin and 9% to albumin.     

The metabolism of the male antifertility agent 1-amino-3-chloropropan-2-ol in the rat

Summary The male antifertility agent 1-amino-3-chloropropan-2-ol (ACP,I) has been shown to be metabolized to-chlorohydrin (III) and metabolites of-chlorohydrin. This accounts for the similar antifertility and renal toxicity effects of both compounds.     

A cannabinoid with cardiovascular activity but no overt behavioral effects

Summary Abnormal-⁸-tetrahydrocannabidiol (ABN-⁸-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.Acknowledgment. This work was supported by NIDA (grant No. DA-00574-01 and DA-00490) and Virginia Heart Society (grant No. RR-05697)     

A centrally induced vasodepressor response after intravenous administration of whole venom ofNaja mossambica pallida in cats

Summary Naja mossambica pallida venom administered i.v. (300 /kg) produces an initial brief fall in blood pressure, due to a direct myocardial depressant effect, and a sustained fall due to central depressant effect.This study was supported by University of Nairobi research grants (670–376). We also thank Mr E. Njogu for photographic assistance.