Release of immunoreactive beta-endorphin in vitro from pituitaries of young and old male rats

Regulation of pituitary beta-endorphin secretion in aging rats: in vitro responsiveness to dopamine

The intermediate lobe of the mammalian pituitary is highly responsive to dopamine inhibition of beta-endorphin secretion. In this study, the ability of aged (12 months) intermediate lobes to respond to dopamine was compared to that of young (6 weeks) tissue, using a short-term in vitro incubation of isolated rat neurointermediate lobes, with measurement of peptide release by radioimmunoassay. Tissue from the aged rats released greater amounts of beta-endorphin peptide than amounts measured from young tissue at all time periods studied. The aged lobes were also found to be significantly more sensitive to dopamine than young glands, as measured by percent change of each group compared to respective baseline release. In comparison, incubation of tissue from young animals in which the intermediate lobe had been acutely denervated by treating rats with injections of the catecholamine neurotoxin, 6-hydroxydopamine, did not differ in responsiveness to dopamine as compared to tissue from control rats. The observations suggest that aging intermediate lobe, while being hypersecretory, is supersensitive to dopamine, perhaps as the result of gradually reduced innervation.

Age-related changes in the contents of neuropeptides in the rat brain and pituitary

beta-Endorphin, Leu-enkephalin, Met-enkephalin, substance P, somatostatin, and cholecystokinin were measured in the brain and the pituitary of male Sprague-Dawley rats aged 3 months, 12 months, and 22 months. beta-Endorphin, Met-enkephalin and Leu-enkephalin contents in the neurointermediate lobe, and the enkephalin levels in the anterior lobe of the pituitary increased with age. The increases in contents were both in the day and at night for beta-endorphin and Met-enkephalin. However, the increase for Leu-enkephalin content was in the day only. Hypothalamic beta-endorphin content decreased with age only in the day. beta-Endorphin and Leu-enkephalin contents in the brain stem, and Leu-enkephalin levels contents in the cortex decreased with age at night. Leu-enkephalin in the striatum decreased with age in the day. There was also an age-related decrease for somatostatin and substance P contents in the striatum and the hypothalamus in the day, and in cholecystokinin levels in the hippocampus, and the hypothalamus at night. It is concluded that there are age differences in neuropeptide levels, and that these changes may differ according to diurnal rhythms.

The elevation of immunoreactive beta-endorphin in old male rats is related to alterations in dopamine and serotonin

The concentration of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP) and the neurointermediate lobe of the pituitary (NIL) was elevated in old as compared to young male rats. Treatment of old male rats with the dopamine precursor, L-DOPA, did not affect the concentration of IR-BE in the AP and produced a significant reduction in the concentration of IR-BE in the NIL. By contrast, administration of the serotonergic neurotoxin, p-CPA, significantly diminished the concentration of IR-BE in the AP of old male rats, while the concentration of IR-BE in the NIL remained unchanged. Hypothalamic IR-BE was decreased in old male rats and was not influenced by administration of L-DOPA or p-CPA. Chromatographic analysis indicated that in the AP of old animals the amount of beta-endorphin relative to beta-lipotropin was increased and was diminished slightly by the treatments. Alterations in IR-BE in the NIL and hypothalamus were represented solely by beta-endorphin. These data suggest that in old male rats, a decrease in dopaminergic activity contributes to the increase in IR-BE levels in the NIL, and an increase in serotonergic function, at least in part, is responsible for the elevation in the level of IR-BE in the AP.

Opioids and the developing organism: a comprehensive bibliography, 1984-1988

A comprehensive bibliography of the literature concerned with opioids and the developing organism for 1984-1988 is presented. Utilized with companion papers (Neurosci. Biobehav. Rev. 6:439-479; 1982; 8:387-403; 1984), these articles cover the clinical and laboratory references beginning in 1875. For the years 1984, 1985, 1986, 1987, and 1988, a total of 877 citations were recorded. A series of indexes accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics, and subdivided into such topics as the type of opioid explored and the general area of biological interest (e.g., physiology).

The importance of striatal interneurons in age-related effects upon potassium- and amphetamine-stimulated dopamine release

The ability of superfused corpus striatal tissue fragments to release endogenous dopamine (DA) in response to potassium (K+ 30 mM) stimulation was significantly attenuated in 18- to 24-month- compared to 2- to 4-month-old male rats. These age-related effects on K+ stimulation were completely abolished with the addition of tetrodotoxin (1 microM) to the superfusion medium. Moreover, no difference in stimulated DA release was obtained between these two age groups following amphetamine stimulation (10 microM).

Cocaine influences beta-endorphin levels and release

Immunoreactive beta-endorphin (IR-BE) was measured in the plasma, anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL) and hypothalamus of male rats treated chronically (once daily for ten days) with cocaine. Cocaine produced a consistent elevation in the concentration of IR-BE in the plasma, the AP and the NIL at doses of 2.5 - 20 mg/kg/ip. The release of IR-BE from the AP and the NIL was determined in vitro and was found to be increased by treatment with cocaine. Chronic administration of cocaine did not affect the concentration of IR-BE in the hypothalamus. Chromatographic analysis revealed that cocaine produced a slight decrease in the amount of beta-endorphin relative to beta-lipotropin in the AP. Beta-endorphin was the major form of IR-BE released by the AP and the sole constituent and secretory product of the NIL. These data indicate that chronic administration of cocaine stimulates the endogenous opiate system, elevating the levels of IR-BE in the pituitary and promoting beta-endorphin release.