Sympatho-inhibitory mechanisms acting at sympathetic ganglia to attenuate hypothalamic-induced pressor effect in the cat

Summary Pressor and tachycardic effects induced in the cat by stimulation of a lateral hypothalamic (LH) site, are shown to be mediated by sympathetic ganglia nicotinic receptor, and potentiated under atropine methyl nitrate sympathetic ganglia blockage. It is postulated that a sympatho-inhibitory pathway muscarinic ganglionic mechanism, co-activated by the LH stimulation, attenuates the pressor and tachycardic effects, the potentiation presumably being a manifestation of blockage of that mechanism.     

Depressor effects of muscarinic and non-muscarinic mediation induced by lateral hypothalamic stimulation in the cat

Transient sympathetically-mediated depressor effects were induced by stimulation of a small locus in the lateral hypothalamic peri-fornical region, medial to the fields of Forel. The ganglionic blocking agent, atropine methyl nitrate (ATMN), was used to show that muscarinic as well as non-muscarinic sympathetic ganglion receptor neurotransmission was involved. Evidence is presented that stimulation of this LH site co-activates a number of mechanisms and that depending on which of these are activated, the ganglionic blocking agent ATMN may either block, reverse or potentiate the depressor effect.     

Depressor effects of muscarinic and non-muscarinic mediation induced by lateral hypothalamic stimulation in the rat

Summary Transient sympathetically-mediated depressor effects were induced by stimulation of a small locus in the lateral hypothalamic peri-fornical region, medial to the fields of Forel. The ganglionic blocking agent, atropine methyl nitrate (ATMN), was used to show that muscarinic as well as non-muscarinic sympathetic ganglion receptor neurotransmission was involved. Evidence is presented that stimulation of this LH site co-activates a number of mechanisms and that depending on which of these are activated, the ganglionic blocking agent ATMN may either block, reverse or potentiate the depressor effect.     

Zur peripheren sympathikushemmenden Wirkung des Clonidins

Summary The influences of clonidine, tetracaine and procaine on the effects of electrical stimulation of the postganglionic sympathetic cardiac nerves have been compared in the isolated perfused rabbit heart. Much lower concentrations of clonidine than of tetracaine were necessary to antagonize the output of noradrenaline and the rise of frequency and contractility. Procaine even in the highest concentration tested did not inhibit the effects of nerve stimulation. In addition to its known central depression of sympathetic tone, clonidine exerts a specific inhibitory action on postganglionic sympathetic neurons.     

Role of alpha and beta adrenoceptors in the regulation of adrenergic neurotransmission in the carotid sinus]

The experiments carried out showed the presence- in sympathetic nerve endings ot the carotid sinus- of alpha and beta adrenoceptors which by means of respective negative and positive feedback processes, modulated NA release induced by a sympathetic nerve stimulation. Similarly, Pgs acted by means of a negative feedback mechanism to regulated adrenergic neuro-transmission in carotid sinus but they could not be considered as the chemical mediators of either alpha or beta adrenoceptors.     

Modulator role of prostaglandins (Pg) in adrenergic neurotransmission in carotid sinus]

In Rabbit carotid sinus, the presence of sympathetic nerve endings capable of releasing noradrenaline has been demonstrated. The release of NA in response to sympathetic nerve stimulation was decreased by PgE2 and a precursor of Pg (arachidonic acid) but was strongly increased by an inhibitor of Pg biosynthesis (indomethacin). The experiments carried out demonstrated that freshly synthesized Pg acts in the same way as exogenous Pg and suggested that Pg could have a regulating effect on adrenergic neurotransmission in carotid sinus. The role of this regulating mechanism in the physiology of carotid sinus has been discussed.     

Changes of the phosphatidylcholine content and the number of synaptic vesicles in relation to the neurohumoral transmission in sympathetic ganglia.

In sympathetic ganglia stimulated in the presence of HC-3, the reduction in number of synaptic vesicles was observed to be accompanied by a significant decrease of the ganglionic phosphatidylcholine content.     

Influence of nocloprost on the vascular responses to various stimuli in the isolated perfused rabbit kidney

Nocloprost, a new synthetic prostanoid, elicited a vasodilator action when given through the renal artery of the isolated perfused rabbit kidney. Lower concentrations of the compound inhibited the pressor response to sympathetic stimulation or to angiotensin II, but potentiated the pressor effect of exogenous noradrenaline. These results were taken as an evidence that nocloprost prevents the release of neurotransmitter by a presynaptic mechanism.     

Cardiac hypertrophy accelerated by left cervical sympathectomy in spontaneously hypertensive rats

Summary Cardiac hypertrophy in spontaneously hypertensive rats was accelerated by denervation of the left cervical sympathetic ganglia. Supersensitivity due to denervation may also exist in cardiac muscles.This work was supported by a grant of the Ministry of Education for 1980.     

Cyclic AMP in neuroblastoma, ganglioneuroma and sympathetic ganglia.

Tissue content of cyclic AMP was as much as 10 times greater in ganglioneuroma than in neuroblastoma. This high cyclic AMP in ganglioneuroma was not significantly different from that of sympathetic ganglia.     

Hypothalamo-hypophyseal-gonadal function in the rat following administration of the novel and selective D-1 agonist CY 208-243

The effects of the novel and selective dopamine D-1 agonist CY 208-243 on the rat hypothalamo-hypophyseal-gonadal (HHG) axis were studied. CY 208-243 did not modify the concentration of luteinizing hormone (LH) in serum from female or male rats, and had no effect upon opiate antagonist-induced stimulation of LH secretion in male rats. CY 208-243 did not inhibit ovulation in cycling female rats. Thus, D-1 receptor activation by systemic drug administration does not alter HHG function in rats.     

Cyclic AMP in neuroblastoma,ganglioneuroma and sympathetic ganglia

Summary Tissue content of cyclic AMP was as much as 10 times greater in ganglioneuroma than in neuroblastoma. This high cyclic AMP in ganglioneuroma was not significantly different from that of sympathetic ganglia.     

Sympathetic, muscarinic vasodilation in cranial vessels of the cat

Pressor responses evoked by stimulation of the preganglionic sympathetic trunk of the feline superior cervical ganglion have been recorded in vivo from the vascular bed perfused by one external carotid and the vertebral artery. When vasoconstrictor activity is blocked and potential vasodilator activity enhanced by close, intracarotid injection of guanethidine and prostaglandin F2 alpha respectively, stimulation evokes a weak pressor response followed, on cessation of stimulation, by a prolonged vasodilation lasting for 6-8 min. The magnitude and duration of the poststimulation vasodilation was reduced significantly by atropine. Due to the prolonged nature of the vasodilation, it is unlikely that a sympathetic cholinergic vasodilation in the classical sense is involved.     

Hypothalamo-hypophyseal-gonadal function in the rat following administration of the novel and selective D-1 agonist CY 208-243

Summary The effects of the novel and selective dopamine D-1 agonist CY 208-243 on the rat hypothalamo-hypophyseal-gonadal (HHG) axis were studied. CY 208-243 did not modify the concentration of luteinizing hormone (LH) in serum from female or male rats, and had no effect upon opiate antagonist-induced stimulation of LH secretion in male rats. CY 208-243 did not inhibit ovulation in cycling female rats. Thus, D-1 receptor activation by systemic drug administration does not alter HHG function in rats.     

Influence of cervical sympathetic nerve stimulation on carotid sinus baroreceptor afferents

Summary In rabbits and dogs, the response of low-threshold carotid sinus baroreceptor afferent fibres to cervical sympathetic nerve stimulation at various non-pulsatile steady pressures was examined. Fibres which possessed a rhythmic bursting discharge at low pressures increased this activity during sympathetic stimulation; all other low-threshold afferents were unaffected.This work was supported by the Medical Research Council of Canada and the British Columbia Heart Foundation.     

Contraction of myoepithelial cells in secreting submandibular glands of dogs.

In slowly secreting submandibular glands of dogs, a sympathetic effect on myoepithelial cells was demonstrated as an acceleration of the flow, followed by retardation, on short-lasting sympathetic stimulation, particularly after beta-adrenoceptor-blocking drugs.     

Influence of nocloprost on the vascular responses to various stimuli in the isolated perfused rabbit kidney

Summary Nocloprost, a new synthetic prostanoid, elicited a vasodilator action when given through the renal artery of the isolated perfused rabbit kidney. Lower concentrations of the compound inhibited the pressor response to sympathetic stimulation or to angiotensin II, but potentiated the pressor effect of exogenous noradrenaline. These results were taken as an evidence that nocloprost prevents the release of neurotransmitter by a presynaptic mechanism.This work was supported by a grant from the Turkish Scientific and Technical Research Council (TAG-578). Nocloprost is the gift of Dr E. Schillinger, Head of Biochemical Pharmacology, Schering AG Research Laboratories, Berlin, FRG.     

Sympathetic,muscarinic vasodilation in cranial vessels of the cat

Summary Pressor responses evoked by stimulation of the preganglionic sympathetic trunk of the feline superior cervical ganglion have been recorded in vivo from the vascular bed perfused by one external carotid and the vertebral artery. When vasoconstrictor activity is blocked and potential vasodilator activity enhanced by close, intracarotid injection of guanethidine and prostaglandin F₂ respectively, stimulation evokes a weak pressor response followed, on cessation of stimulation, by a prolonged vasodilation lasting for 6–8 min. The magnitude and duration of the poststimulation vasodilation was reduced significantly by atropine. Due to the prolonged nature of the vasodilation, it is unlikely that a sympathetic cholinergic vasodilation in the classical sense is involved.     

The effect of gonadotrophins on the steroidogenesis, in the ovary and testis of gonadotrophin-deprived fresh water teleost, Cyprinus carpio.

Studies have been made on the effect of LH, FSH, and LH+FSH on the gonadal steroidogenesis in gonadotrophin-deprived common carp. LH alone and in combination with FSH was more effective than FSH in stimulation of steroidogenesis.     

Similarity between the effects of suprachiasmatic nuclei lesions and of pinealectomy on gonadotropin release in ovariectomized,sulpiride-treated and melatonin-replaced rats

The aim of this study was to compare the effects of pineal indole treatments on LH and FSH release in pinealectomized and suprachiasmatic lesioned and ovariectomized rats rendered hyperprolactinemic by acute sulpiride treatment. pinealectomy or suprachiasmatic nuclei lesions in female rats both decreased plasma LH and FHS at 10, but not at 20 d after surgery, whereas the daily afternoon administration of melatonin effectively restored levels of both gonadotropins to control values. In ovariectomized rats, pinealectomy or suprachiasmatic nuclei lesions were ineffective in counteracting the high plasma levels of LH and FSH. However, sulpiride treatment in both pinealectomized and suprachiasmatic nuclei lesioned and castrated female rats significantly decreased the levels of LH and FSH, an effect which was counteracted by daily afternoon melatonin administration. Other pineal indoles tested, i.e., 5-hydroxy- and 5-methoxytryptophol, were ineffective in regulating gonadotropin levels. The results suggest that the pineal gland, through its hormone melatonin, can modulate gonadotropin secretion by acting on a dopamine mechanism independent of hypothalamic suprachiasmatic areas.