Effect of beta-endorphin and naloxone on rat testicular steroidogenesis.

With a view to examine the possibility of a direct role of opioids in the regulation of testicular steroidogenesis, the following in vivo and in vitro experiments were conducted in male rats of different age groups. Intratesticular (i.t.) injections of beta-endorphin (beta-EP) and its antagonist naloxone (nal) were given bilaterally to adult (80-100 days), peripubertal (40 days) and juvenile (20 days) rats and blood was collected at different time intervals up to 90 min and assayed for testosterone (T). beta-EP suppressed T levels in all age groups of rats while naloxone stimulated T secretion only in adult rats. In another experiment, adult rats were also injected with 60 IU of hCG (sc) after 30 min. of beta-EP/nal treatment. Naloxone induced a greater rise in T in the presence of hCG while beta-EP blocked the hCG induced rise in testosterone. In the in vitro sets of experiments, isolated interstitial cells from testes of adult, 40 and 20 days old rats were incubated for 4 hr with hCG (25 IU), beta-EP (0.5ng) and nal (5.0ng) alone or in combinations. Naloxone alone was ineffective although it significantly enhanced hCG stimulated T release. beta-EP decreased both basal and hCG stimulated T release. Based on these results we postulate that opioids may influence steroidogenesis possibly by altering the response of interstitial cells to LH.

Effects of post-training ß-endorphin and Met-enkephalin administration on two-way active avoidance task in well-nourished and protein malnourished rats

Protein malnutrition during suckling period or throughout the life affects the hypothalamic ß-endorphinergic system of adult rats. In the present study, rats were under nourished during suckling by feeding their dams an 8% casein diet whereas well-nourished dams recived a 25% casein diet from birth until weaning (21 day of postnatal life). After weaning, the offsprings were maintained with the same diet as their dams. When rats were 3 month-old, they were subjected to two-way active avoidance task. Protein malnutrition did not affect the performance in the two-way active avoidance task. Post-training ß-endorphin or Met-enkephalin administration impaired the retention of shuttle avoidance tast in both well-nourished and undernourished rats. However, the amnesic effect of the peptides was only achieved in undernourished rats with higher doses of apioids when compared to the well-nourished rats. These data suggest that undernourished rats present alterations in opioid sensitivity which may be related to changes in the levels of ß-endorphin previously observed both in brain and hypothalamus of early undernourished adults rats

Age-related changes in the neuromodulatory effect of opioid peptides on sympathetic nerve terminals

A alteraçäo, dependente da idade, do efeito neuromodulador da ß-endorfina nos terminais nervosos simpáticos foi estudada na porçäo prostática de vasa diferentia de ratos de 4 e 20 meses. O efeito da ß-endorfina e naloxona sobre a contraçäo induzida pelo estímulo transmural dos terminais nervosos (0.2 Hz, 0.5 ms, metade da voltagem supramáxima) foi analisado. Na ausência da droga näo ocorreram alteraçöes dependentes da idade na contraçäo induzida pelo estímulo nervoso. ß-Endorfina causava inibiçäo dose-dependente da contraçäo muscular. A sensibilidade da inibiçäo pela ß-endorfina duplicava entre 4 e 20 meses. Naloxona potenciava de maneira dose-dependente as contraçöes campo-estimuladas induzidas. A potência da naloxona era seis vezes maior em animais de 20 do que de 4 meses. Os dados deste trabalho säo comparados com as alteraçöes relacionadas à idade na reatividade pós-juncional, e é proposto o desenvolvimento de mecanismos compensatórios da idade no nível pré-juncional

ß-endorphin and electroconvulsive shock alter the retrieval of two avoidance tasks when given after the first, but not the second, training session

1. Rats were submitted to three consecutive sessions, one sessions per day, of two-way active avoidance or of step-down inhibitory avoidance, and received 1 µg/Kgß-endorphin intraperitoneally or an electroconvulsive shock immediately aftere the first or after the second training session. 2. Administration of either treatment after the first session caused a reduction of performance in the second session in both tasks. There was no impairment of performance in the third session. 3. Administration of either treatment after the second session did not affect performance during the third session. 4. Therefore the effect of ß- endorphin and of electroconvulsive shock on active and inhibitory avoidance performance was expressed only when treatments were administered after the first, i.e., novel, training experience. We suggest this effect is on mechanisms acting on retrieval, since the retention performance of all groups for the third session were identical