Summary1. The pharmacological properties of an anthelmintic, pyrantel, and some of its analogues have been described and compared with piperazine in a variety of vertebrate and helminth preparations. 2. Pyrantel and its analogues in common with nicotine and decamethonium cause spastic paralysis in chicks and contracture of the chick semispinalis and toad rectus abdominis muscles. 3. In the soleus and anterior tibialis muscles of the cat, pyrantel in large amounts caused a short-lived neuromuscular block that was preceded by initial depolarization. 4. In preparations from cat and rat, pyrantel showed properties common to both competitive and depolarizing neuromuscular blocking drugs. 5. Pyrantel blocked the contracture evoked by transmural stimulation and caused a marked contracture of the worm. Piperazine caused a gradually developing reduction in the responses to transmural stimulation and no contracture.6. Pyrantel and its analogues caused a slowly developing contracture of strip preparations of Ascaris, being more than 100 times more active than acetylcholine in this respect. Piperazine caused a relaxation of Ascaris strip preparations and in common with (+)-tubocurarine blocked the responses to acetylcholine and pyrantel analogues on this preparation. 7. Pyrantel caused depolarization and increased spike discharge frequency in single muscle cells of Ascaris, these changes being accompanied by increase in tension. Piperazine, on the other hand, caused hyperpolarization and reduction in spike discharge frequency and relaxation, and antagonized the effects of pyrantel.

Results: Six distinct branching patterns were observed. The majority (82.9%) of middle cerebral arteries studied conformed to the typical bifurcating vessel commonly referred to in the literature. However, the

KentThe mechanical and electrophysiological activity of rings and strips of thoracic aortic smooth muscle taken from normotensive, DOCA-hypertensive and New Zealand spontaneously hypertensive (A.S. strain) rats have been compared. Aortae from A.S.-hypertensive rats developed less tension in the presence of noradrenaline and K+ than those isolated from normotensive and DOCA-hypertensive rats. Aortae from DOCA-hypertensive rats developed the same tension in response to K+ as normotensive rats but were less reactive to noradrenaline. Measurements of resting membrane potentials from the three groups of rats demonstrated that whereas normotensive and DOCA-hypertensive rats had similar resting membrane potentials, those from A.S.-hypertensive rats were significantly lower (P<0.001). It is suggested that the enhanced responsiveness of intact vascular beds in A.S.-hypertensive rats is a consequence of a change in the geometry of the blood vessels rather than an increase in the contractor response of the smooth muscle cells. Pickering (1955) concluded that arterial pressure behaved like a graded characteristic so far as inheritance was concerned, with hypertensives constituting the righthand tail of a normal distribution curve. Clearly, the New Zealand strain of rats with genetical hypertension offered an opportunity to study the pathogenesis of a spontaneously occurring hypertension which might well have analogies with essential hypertension in man.Initially, Laverty & Smirk (1961) (Lessin, 1965) on at least 2 separate days before the experiment.

The Na(+), K(+) and Ca(2+) content of plasma and aortic vascular smooth muscle from normotensive and A.S.-hypertensive rats have been compared. There was no significant difference in the plasma concentrations of Na(+), K(+) and Ca(2+), or the Na(+), K(+) and water content or (3)H-inulin space of aortic tissue in the two groups.There was a marked increase in the amount of Ca(2+) in the aortae taken from the hypertensive animals as compared with the normotensive animals (P<0.01).

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