The ultrastructural characteristics of the arcuate nucleus and median eminence in rats have been studied by means of formaldehyde-osmium tetroxide fixation method. The observations showed that there are two kinds of neurons (dark and light) in the arcuate nucleus which might be responsible for producing both dopamine and releasing hormones. The tanycytes of the ependyma of the third cerebral ventricle pass longitudinally through the various zones of the median eminence and reach at pericapillary space of the portal vessels. The neurosecretory substance-containing nerve terminals may travel between ependymal cells and even enter the cavity of the third ventricle or end around the basal membrane of the capillaries of the median eminence. The axo-somatic and axodendritic synapses are formed at the perikaryon and dendrites of neurons in the arcuate nucleus. Both agranular type and granular type of axo-axonic synapses are encountered in the fibrous zone of the median eminence. There are also synaptic connections between the basic processes of tanycytes and the large granular vesicle-containing nerve terminals in the palisade zone of the median eminence. The ultrastructural characteristics mentioned above suggest that (1) the releasing (or inhibiting) hormones of the hypothalamus might be released through two routes: into the portal capillaries from nerve terminals directly or into the cerebrospinal fluid of the third ventricle first and uptaken by tanycytes, then transported to the portal capillaries by the basic processes of tanycyte; (2) each step of synthesis, storage, transport and release of the releasing (or inhibiting) hormones could be regulated by nervous mechanism.
By86RbCl-extraction method, the effects of tetrandrine (Tet), verapamil (Ver) and propranolol (Pro) on myocardial blood flow of mice were studied. Both I.P. Tet 100 mg/kg and Ver 5 mg/kg increased the blood flow, whereas I.P. Pro 30 mg/kg did not. Pro counteracted significantly the increase of myocardial blood flow by isoproterenol, while Tet and Ver failed. On the other hand, Tet and Ver markedly antagonized the increase of myocardial blood flow by CaCl2, but Pro did not.
The results indicate that unlike the β-receptor blocking agent Pro, Tet may be a calcium antagonist similar to Ver.
The antagonistic effects of tetrandrine (Tet) on ouabain-induced contraction were studied in swine coronary arterial strips.
Like verapamil (Ver), the contraction evoked by ouabain (Oub) 0.85 μM, the synergistic effect of Oub 85 nM and Ca++ 2–16 mM, and the response to electrical stimulation in the presence of Oub 85 nM were all inhibited by Tet (10 μM-1.2 mM), although these effects were less potent than those of Ver.
All these pharmacological actions of Tet and Ver were reversed by the addition of extra Ca++ to the bathing medium.
The results we obtained confirm that Tet is a Ca++-antagonist of plant origin.