Sympathetic innervation of mammary glands mediates suckling-induced reflex inhibition of milk yield in rats.
Previous work has shown that physiologic activation of the sympathetic system may inhibit milk yield (ME) in rats. Thus, adrenal catecholamines (CAs) are released by suckling, but it is not known whether such inhibition results also from reflex activation by the same stimulus of neural sympathetics upon the mammary gland. The present experiments were designed to determine whether suckling inhibits ME induced by oxytocin (OT) in the urethane-anesthetized lactating rat, and whether such inhibition results from adrenal and/or neurally released CAs. Rats were isolated (6 h) from their pups and then anesthetized. OT (0.8 mU every 2 min) was administered intravenously to the mothers during suckling. Rats were either chronically implanted with cannulae into the lateral cerebral ventricles (intracerebroventricularly), bilaterally adrenalectomized (ADX), hypophysectomized (HX), spinal cord transected (SCT: T3-T4), or had the nipple area (NA) locally anesthetized before suckling. MEs were low in control, sham, ADX and HX rats, but not in rats given the beta-adrenergic blocker propranolol (PROP; intravenously or intracerebroventricularly injected), nor in SCT, NA or PROP-HX rats. As revealed by ductal resistance measurements as an indicator of ductal tone, suckling-induced inhibition of ME was due to ductal constriction within the mammary glands. These effects of suckling, however, could be prevented by prior activation of ductal mechanoreceptors. Together, these results indicate that suckling inhibits ME through the reflex activation of neurally mediated central beta-adrenergic mechanisms, and that these effects, in turn, can be regulated by ductal mechanoreceptor activation.
Morales
T
T
Centro de Neurobiología, Universidad Nacional Autónoma de México, Campus UNAM, Apdo. Postal 1-1140 76230 Juriquilla, Querétaro, Qro., Mexico.
Shapiro
E
E
Marina
N
N
Mena
F
F
D000315:Adrenalectomy; D000322:Adrenergic Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018674:Adrenergic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000772:Anesthesia, Local; D000818:Animals; D001940:Breast / Q000187:drug effects / Q000294:innervation*; D003655:Decerebrate State / Q000503:physiopathology; D005260:Female; D007016:Hypophysectomy; D007774:Lactation; D008465:Mechanoreceptors / Q000187:drug effects; D008892:Milk / Q000378:metabolism*; D009558:Nipples / Q000187:drug effects / Q000502:physiology; D010121:Oxytocin / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; D010121:Oxytocin