The response of the circular muscle layer of the guinea-pig isolated vas deferens to transmural electrical stimulation.

1 Four preparations are described for the isolation of the response of the circular muscle of the guinea-pig vas deferens. These are the ;Furchgott' strip, the ;Vane' strip, the chain preparation and the perfused preparation.2 The four preparations were stimulated transmurally with pulses of supramaximal voltage. The threshold pulse width to which the strips and the perfused preparation responded was 0.025 ms and the maximum responses occurred at 0.1 ms. The threshold frequency was 2 Hz for strip and perfused preparations, the maxima being 20 or 50 Hz for strip preparations and 100 Hz for perfused preparations. The effect of varying the number of pulses per train was also investigated on the perfused vas. Responses occurred to train lengths of 8, 16, 32, 128 pulses, the maximum response being given at 128 pulses at 100 Hz; 256 pulses per train did not produce a further increase in response. The perfused preparation exhibited an after-response at certain frequencies and train lengths.3 Tetrodotoxin and the local anaesthetics, procaine and lignocaine, reversibly abolished the responses of strip and perfused preparations to transmural stimulation.4 The response to intramural nerve fibre stimulation was abolished by guanethidine or bethanidine; this abolition was reversed by dexamphetamine. Noradrenaline contracted strip preparations of circular muscle and raised the pressure in perfused preparations; noradrenaline was competitively antagonized by thymoxamine. The major part of the motor innervation of the circular layer seems to be noradrenergic.

The isolated circular muscle layer of the vas deferens of the guinea-pig.

1 A method is described for the removal of the outer longitudinal layer of muscle from the guinea-pig isolated vas deferens. The remaining tube of circular muscle was perfused at constant flow for recording changes in pressure in response to transmural electrical stimulation or to drugs. 2 The response to transmural stimulation was a rise in perfusion pressure at frequencies of stimulation of 5 to 50 Hz for trains of 16 to 256 pulses. At some frequencies and train lengths a second rise in pressure (the after-response) occurred after the cessation of the stimulus train. 3 Perfused vasa stripped of their longitudinal muscle did not develop longitudinal tension on electrical stimulation nor on intraluminal or extraluminal exposure to agonists. 4 Stripped perfused vasa gave concentration-dependent pressure rises to noradrenaline but not to acetylcholine. 5 Responses to transmural stimulation and to noradrenaline were antagonized by thymoxamine. Cocaine or desmethylimipramine increased the duration of the after-response to transmural stimulation. Reserpine pretreatment almost abolished the response and after-response. The after-response, but not the response, was increased by physostigmine and antagonized by atropine. 6 The results are discussed in relation to the known histochemical and electronmicroscopical demonstrations of dense noradrenergic and cholinergic populations of nerve terminals in the circular layer. It is suggested that mechanisms may exist for the separate control of the longitudinal and circular layers as a basis for propulsive activity.

The distribution of arachidonic acid in plasma and tissues of patients near term undergoing elective or emergency Caesarean section.

The distribution of arachidonic acid in both the free and the bound state was measured in the maternal circulation, the fetal circulation and tissues within the pregnant uterus in 16 patients undergoing Caesarean section. Half of the patients had an elective Caesarean section and half had a Caesarean section during labour. No differences in arachidonic acid concentrations were found between the maternal or fetal circulations in women having elective Caesarean section and those having a Caesarean section in labour. The total and bound values of arachidonic acid in myometrium were higher in patients undergoing Caesarean section in labour. There was also an increased amount of arachidonic acid when expressed as an arachidonic acid/palmitic acid ratio between the fetal circulation and the maternal circulation, suggesting an active transport mechanism for arachidonic acid across the placenta. Levels of free arachidonic acid were in microgram quantities in both plasma and tissues, suggesting that the availability of free arachidonic acid was not the limiting factor in prostaglandin production.