Mechanisms of action of dopamine in the peripheral nervous system of chicks and rats

Acute injections of corticosterone, norepinephrine and epinephrine retards food passage in the crop of chicks

The purpose of the present study was to clarify whether acute injection of stress-related hormones, corticosterone (CORT), norepinephrine (NE) and epinephrine (E) affect food passage in the crop of chicks (Gallus gallus). Subcutaneous (SQ) injection of CORT significantly retarded the food passage in the crop of chicks. Intraperitoneal (IP) injection of NE and E also significantly decreased the crop emptying rate. Additional experiments by using agonists of adrenergic receptors found that IP injection of phenylephrine and clonidine but not isoproterenol retarded the food passage in the crop of chicks. These results demonstrated that the effect of NE and E would be mediated by alpha-1-, alpha-2- rather than beta-adrenergic receptor. Finally, we found that injection of CORT, NE and E had no effect on the number of defecations while intracerebroventricular injection of corticotropin-releasing hormone and urocortin-3 significantly increased it. These results suggest that CORT, NE and E might affect the food passage in the upper digestive tract in chicks.

Tramadol inhibits rat detrusor overactivity caused by dopamine receptor stimulation

PURPOSE

In patients with Parkinson's disease an imbalance between stimulatory D2-like receptors and inhibitory D1-like receptors may contribute to detrusor overactivity. Apomorphine, which stimulates D1-like and D2-like dopamine receptors, induces detrusor overactivity in rats. Tramadol is an analgesic drug that stimulates opioid receptors and inhibits reuptake of serotonin and noradrenaline. To evaluate a potentially inhibitory effect of tramadol the drug was given to rats with apomorphine induced detrusor overactivity.

MATERIAL AND METHODS

Female Sprague-Dawley rats were used. During anesthesia catheters were introduced into the bladder dome, femoral vein and subcutaneously (SC). Three days later the rats were placed in a metabolism cage and voiding was stimulated by infusing saline into the bladder. Micturition parameters were recorded and compared after the administration of apomorphine and tramadol or vehicle. Desmopressin was given as pretreatment to suppress the diuresis produced by tramadol.

RESULTS

While 30 microg kg-1 apomorphine SC was devoid of effect, 60 and 100 microg kg-1 apomorphine SC induced a transient detrusor overactivity. Tramadol (1 mg kg-1) was without effect but 5 and 10 mg kg-1 tramadol intravenously attenuated the effects of apomorphine, while inducing prominent diuresis. Pretreatment with desmopressin, which did not alter cystometry or the effects of apomorphine, abolished diuresis. In these rats 5 and 10 mg kg-1 tramadol intravenously abolished the overactivity caused by apomorphine SC.

CONCLUSIONS

Tramadol effectively suppresses apomorphine induced detrusor overactivity in doses shown to have analgesic activity. Hence, tramadol may provide an approach to treat lower urinary tract disorders in which dopamine receptor activation is involved.