Effect of neonatal androgenization on the testosterone feedback sensitivity in adult rats in two lighting conditions

Neonatally androgenized and intact adult male Wistar rats received daily, during 1 week, either testosterone propionate or sesame oil injections in periodic or constant light. Serum and pituitary gonadotropins and hypothalamic LHRH were measured. In periodic light, neonatal androgenization did not change the serum concentration or pituitary contents of gonadotropins, or the hypothalamic content of LHRH. Testosterone injections decreased serum concentration and pituitary content of gonadotropin of intact rats but failed to decrease the pituitary gonadotropin content of neonatally androgenized rats. In constant light, serum FSH was decreased in neonatally androgenized rats. Testosterone injections decreased both serum LH and FSH concentrations of intact rats but only serum LH of androgenized rats. Pituitary gonadotropin and hypothalamic LHRH contents remained unchanged. We conclude that neonatal androgenization renders the male rat hypothalamo-pituitary axis more resistant to changes of testosterone concentration in adulthood. Constant light did not sensitize the neonatally androgenized rats to testosterone, but on the contrary, testosterone injections were less effective in constant than in periodical light.     

Influence of testosterone on autotomy in castrated male rats

Sex-related differences exist in nociception and gonadal steroids influence the analgesic response in animals and humans. As we have shown previously, estrogen could modify autotomy in female rats using the sciatic nerve transection model. To further characterize the relationship between gonadal steroid and nociception, the role of testosterone on autotomy in sciatic nerve sectioned rats was investigated. Twenty male rats were subjected to orchiectomy (ORX). Then ten rats received subcutaneous sesame oil and the other ten were treated with testosterone propionate in sesame oil (TP; 500 microg/day/rat). All the rats underwent sciatic nerve resection in left hind limb. Degree of self-mutilation was measured daily for 8 weeks. TP reinstatement resulted in significantly lower autotomy scores in orchiectomized rats. The results demonstrated that testosterone could modify the autotomy behavior, an indicator of neuropathic pain, in rats after nerve injury.     

The effect of testosterone on serum gonadotropins of castrated rats kept under different lighting conditions.

Testosterone feedback sensitivity was measured as the ability of testosterone propionate to decrease serum LH and FSH of long-term castrated (4 wk) rats under four different lighting conditions: periodic light (12L:12D), constant light (LL), constant darkness (DD), and dim night illumination (1 lx) with a 12L:12D photoperiod. Rats were exposed to the different lighting conditions for 1 wk, during which they received daily testosterone propionate (125 micrograms or 250 micrograms s.c.). At the end of the experiment the rats were decapitated at 1100 h, and serum gonadotropin levels were measured by RIA. Serum LH of the rats kept under LL was reduced to the level of the intact rats with the smaller testosterone dose (125 micrograms/day). Under all other lighting conditions only the large dose (250 micrograms/day) was able to restore the serum LH concentration to the level of the intact rats. Serum FSH was restored only partially, and the effect was the same with both doses and similar under all lighting conditions. We conclude that the increase in testosterone negative feedback sensitivity was not caused by the lack of periodicity of illumination alone, but that sufficient intensity of lighting throughout the 24 h was needed as well.     

Neurotransmitters and estrogen interact to affect beta-endorphin levels in castrated female rats

The possibility of an interaction between neurotransmitter systems and estrogen in affecting levels of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP), the neurointermediate lobe of the pituitary (NIL) and the hypothalamus was investigated in ovariectomized (OVX) female rats. Chronic administration of the dopamine antagonist, haloperidol (HALO), had no effect on IR-BE levels in the AP. By contrast, the content of IR-BE in the NIL was increased and the content of IR-BE in the hypothalamus was decreased by HALO. Chronic treatment with estradiol benzoate (EB) produced a decrease in IR-BE in all three tissues. The effect of EB on IR-BE levels in the AP and NIL was reversed by administration of HALO, while EB and HALO appeared to act independently on the hypothalamus. Gel chromatography indicated that alterations in IR-BE in the AP corresponded to similar changes in beta-endorphin (BE) and beta-lipotropin (LPH) and that BE alone comprised the immunoreactivity detected in the NIL and hypothalamus regardless of treatment. Chronic treatment with the alpha-adrenergic agonist, clonidine (CLON), increased, whereas treatment with EB decreased, IR-BE levels in the AP, NIL and hypothalamus. EB attenuated the effect of CLON on IR-BE levels in the AP and hypothalamus. Chronic treatment with CLON appeared to promote the formation of BE in the AP, whereas the proportions of BE and LPH were similar in the AP of controls and animals treated with EB or EB and CLON. BE alone was detected in the NIL and hypothalamus of treated and control animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short- and long-term effects of testosterone on diaphragm in castrated and normal male rats

Prezant, David J., Manoj L. Karwa, Helen H. Kim, DianeMaggiore, Virginia Chung, and David E. Valentine. Short- and long-term effects of testosterone on diaphragm in castrated and normalmale rats. J. Appl. Physiol. 82(1):134-143, 1997.The effects of short- and long-term testosteroneabsence or treatment on the diaphragm were studied in castrated andsexually normal male rats. Compared with control rats (untreated normalmales), testosterone absence or treatment did not significantly affect costal weight. In untreated castrated males, there were significant decreases in specific forces, type II fiber cross-sectional area, andmyosin heavy chain (MHC) isoform 2B after 2.5 wk. In castrated malesthat received testosterone, there were significant increases inspecific forces, type II total fiber proportional area, and relativeexpression of all adult diaphragm fast MHC isoforms(MHC-2_all) after 2.5 wk. In normal males thatreceived testosterone, the only significant finding was an increase inMHC-2B after 2.5 wk. Across all groups, there was close correlationbetween increases in maximum tetanic forces and MHC-2_all.Changes in diaphragm function and composition were closely related tochanges in serum testosterone levels at 2.5 wk. The lack of significantchange in diaphragm function at 10 wk occurred despite changes in serumtestosterone levels and diaphragm composition similar to those at 2.5 wk. These findings support our hypothesis that the effects oftestosterone are dependent on basal circulating androgen levels andstudy duration.

     

The prostate response to prolactin modulation in adult castrated rats subjected to testosterone replacement

Despite the androgenic dependence, other hormones, growth factors, and cytokines are necessary to support prostatic growth and maintain the glandular structure; among them, prolactin is a non-steroidal hormone secreted mainly by the pituitary gland. However, extra-pituitary expression of prolactin, such as in the prostate, has also been demonstrated, highlighting the paracrine and autocrine actions of prolactin within the prostate. Here, we investigated whether prolactin modulation alters ventral prostate (VP) morphophysiology in adult castrated rats. Sprague Dawley rats were castrated and after 21 days, divided into ten experimental groups (n?=?6/group): castrated control: castrated animals that did not receive treatment; castrated+testosterone: castrated animals that received T (4 mg/kg/day); castrated+PRL (PRL): castrated animals receiving prolactin (0.3 mg/kg/day); castrated+T+PRL: castrated animals that received a combination of testosterone and prolactin; and castrated+bromocriptine (BR): castrated animals that received bromocriptine (0.4 mg/kg/day). The control group included intact animals. The animals were treated for 3 or 10 consecutive days. At the end of experimental period, the animals were euthanized, and the blood and VP lobes were collected and analyzed by different methods. The main findings were that the administration of prolactin to castrated rats did not exert anabolic effects on the VP. Although we observed activation of downstream prolactin signaling after prolactin administration, this was not enough to overcome the prostatic androgen deficiency. Likewise, there was no additional glandular involution in the castrated group treated with bromocriptine. We concluded that despite stimulating the downstream signaling pathway, exogenous prolactin does not act on VP in the absence or presence of high levels of testosterone.     

Initiation of copulatory behavior in castrated male rats injected with critically adjusted doses of testosterone

In castrated male rats it was possible by means of administration of adequate testosterone propionate doses to induce a state in which the males did not initiate copulatory behavior with a stimulus female displaying no (Lordotic female) or weak (Presenting female) intensity of precopulatory behavior. On the other hand, such males started to copulate and finished copulatory series when a stimulus female exhibiting the complete pattern of precopulatory behavior (Darting female) was offered. The males “prepared” in this manner displayed regularly precopulatory behavior directed toward all the stimulus females. The requisite testosterone doses differed individually. However, in the majority of cases they were in the range of 500–700 μg of testosterone injected once a week.     

Effects of testosterone metabolites on copulation and medial preoptic dopamine release in castrated male rats

The medial preoptic area (MPOA) is an important integrative site for male sexual behavior. Dopamine (DA) is released in the MPOA of male rats shortly before and during copulation. The recent presence of testosterone (T) may be necessary for this precopulatory increase in release. Previously, the postcastration loss of copulatory ability mirrored the loss of the DA response to an estrous female, and the restoration of copulation with exogenous T was concurrent with the reemergence of this DA response. The present study investigated the effectiveness of the two major metabolites of T in maintaining copulation and basal and female-stimulated DA levels. Adult male rats were castrated and received daily injections of estradiol benzoate (EB), dihydrotestosterone benzoate (DHTB), EB + DHTB, testosterone propionate (TP), or oil vehicle for 3 weeks. Microdialysis samples were collected from the MPOA during baseline conditions, exposure to an estrous female behind a barrier, and copulation testing. EB + DHTB- and TP-treated animals had normal basal DA levels and showed a precopulatory DA response, and most copulated normally. EB-treated castrates had high basal DA levels, but failed to show a female-stimulated increase; most intromitted, but none ejaculated. DHTB- and oil-treated groups had low basal levels of extracellular DA that did not increase during copulation testing; most failed to mount and none ejaculated. These results suggest that E maintains normal basal levels of extracellular DA in the MPOA, which are sufficient for suboptimal copulation, but that androgen is required for the female-stimulated increase in DA release and for facilitation of ejaculation.     

Effects of testosterone and estradiol on ventral prostate and body weights of castrated rats

Administration of 100 μg of testosterone (T) daily for 14 and 28 days to 7-day castrate rats restored the weight of the ventral prostate to a level which slightly exceeded that of the controls. Ventral prostate weight in groups receiving estradiol-17β (E₂) doses of 10, 50, 100, 200, or 500 μg administered simultaneously with 100 μg of T did not differ significantly from intact controls, although the weights were lower at E₂ levels greater than 100 μg. Body weights of the castrated rats receiving 100 μg of T did not differ from those of sham castrated controls. However, mean body weights of all groups which received E₂ (10 to 500 μg) simultaneously with 100 μg of T were significantly less than (p< .025 or less) those of the sham castrated controls. Analysis of normalized ventral prostate weights, i.e., mg ventral prostate/100 gm body weight, showed that E₂ does not antagonize T and revealed a trend which suggested that low levels of E₂ (10, 50 and 100 μg) may have enhanced the restorative effects of 100 μg T. Our data indicate that 100 μg of T approaches a physiological dosage for castrated rats and that in contrast to the possible enhancement of its restorative effects on the ventral prostate by low leve E₂, its body weight stimulating effects are clearly impaired by E₂.