The impact of alcohol ingestion on erections in rats as measured by a novel bio-assay

Ultrastructural comparison of penile cavernous tissue between hypertensive and normotensive rats

Our aim was to compare the ultrastructure of penile cavernous tissue in the spontaneous hypertensive rat (SHR) and normotensive rat, and study the relation of blood pressure with erectile function. After injection of apomorphine (APO), penile erectile frequency in 16-week-old SHR (group A) and Wistar-Kyoto rat (WKY) (group B) was observed and noted. The ultrastructure of the penile cavernous tissue was studied by scanning electron microscope and transmission electron microscope. The mean blood pressures were significantly higher in group A than in group B (P=0; 171.20+/-10.94 and 117.60+/-12.38, n=5, for group A and group B, respectively). After treatment of the two groups with APO, the erectile frequency in group A was significantly less than in group B (P=0.007; 0.40+/-0.55 and 2.40+/-1.14, n=5, for group A and group B, respectively). Significant ultrastructural pathological changes were observed in the tunica albuginea and penile cavernous tissue of SHR. The elastic fibers were decreased and the collagen fibers of the sinusoid were increased in group A. The tunica albuginea thickness (mean+/-s.d.) was 100.20+/-7.22 microm and 126.00+/-7.65 microm in group A and group B, respectively. The tunica albuginea of group A was significantly thinner than that in B (P=0.001). Some endothelial cells and smooth muscle cells exhibited damaged mitochondria, and endoplasmic reticulums and Schwann cells were degenerated in group A. Although the function of penile erection might be affected by a secondary effect related to endothelial dysfunction of hypertension, these ultrastructural pathological changes of the penile cavernous tissue might also be one of the important mechanisms of erectile dysfunction caused by hypertension.

Prepubertal genital grooming and penile erections in relation to sexual behavior of rats

The development of genital grooming (GG) and spontaneous penile erections (SPE) was evaluated in socially housed male rats from 25 to 47 days of age, and their sexual behavior was tested from 42 to 74 days of age. GG was the first behavior that appeared (27 days of age) prior to SPE (44 days of age). The values of frequency and duration of GG and SPE showed a gradual increase as puberty was reached. The mean age in which copulatory responses were first observed were: 54.5 days of age for mounts, 55 days of age for intromission and 59 days of age for ejaculation. The proportion of GG bouts that were followed by SPE showed a gradual increase throughout the recording days. A high correlation was found between the early onset and higher frequency of GG and an early onset of sexual behavior. Similarly, higher frequency and/or longer duration of SPE were correlated with an early onset and a better performance of sexual behavior. These results are consistent with previous studies, which suggest an important role of GG on the manifestation of sexual behavior; moreover, considering the high correlation between the occurrence of SPE and sexual behavior, it is possible that, as GG, SPE play an important role in the readiness of adult male rats for reproduction.

Neuropeptide Y (NPY) levels in alcoholic and food restricted male rats: implications for site selective function

Neuropeptide Y (NPY) has been implicated in the control of ingestive, cardiovascular, and reproductive function. Blood pressure and sexual function were examined in Long-Evans rats receiving 6% ethanol-containing or calorically matched liquid diets, or rat chow ad lib. After 12 weeks of exposure, rats were sacrificed and plasma hormone levels and NPY content of microdissected brain regions were determined. Neither long-term alcohol ingestion nor caloric restriction were associated with major decrements in copulatory behavior. Long-term alcohol ingestion was associated with decrements in erectile function ex copula. Long-term alcohol ingestion was also associated with: (i) a moderate degree of hypertension; (ii) a failure to gain weight; (iii) decrements in circulating levels of LH, testosterone, and ACTH (but not progesterone); and (iv) increased corticosterone levels. Long-term alcohol ingesting and calorically-restricted rats exhibited alterations in daily feeding patterns. These physiological changes in response to long-term alcohol ingestion or caloric restriction were associated with neural site-selective differences in NPY content. Elevated NPY in the paraventricular nucleus was associated with voluntary (as in alcohol ingestion) or involuntary (as in caloric restriction) reductions in food intake. Differences in NPY in the suprachiasmatic and ventromedial nuclei were associated with the differences in feeding patterns. The decrements in hormone levels were associated with higher levels of NPY in the median eminence and in the arcuate nucleus.

Apomorphine versus mating behavior in testing erectile capabilities of diabetic rats

OBJECTIVES

Diabetes mellitus (DM) is an important cause of organic impotence. It is estimated that 35% to 75% of diabetic patients are impotent. In the present study we investigated the effect of experimentally induced diabetes (streptozocin 60 mg/kg, intraperitoneally, for 9 weeks) on sexual behavior and compared it to the apomorphine (APO) bioassay test.

METHODS

Libido, genital reflex excitability, and penile competence as measured by different parameters of mating behavior were reduced with DM (P < 0.05 versus control for each parameter).

RESULTS

Of 17 diabetic rats, 53% (9 rats) experienced positive mating behavior (either intromission or ejaculation) compared with 82.4% (14 rats) positive response to the APO bioassay test. Moreover, combined apomorphine injection and mating sexual testing in diabetic rats that achieved intromission but not ejaculation or those that did not achieve intromission in the initial mating, considerably improved the performance of these rats.

CONCLUSIONS

We suggest that the APO test alone or, even better, combined APO injection and sexual testing are superior in eliciting maximum erectile capabilities of the diabetic rats than mating testing alone.

Effects of streptozotocin-induced diabetes on dopaminergic functioning in the rat: analysis of yawning behavior

Apomorphine, a dopamine receptor agonist, causes yawning in rats. It has been suggested that the analysis of yawning behavior provides an index of dopamine autoreceptor function. Dopamine turnover in the substantia nigra of diabetic rats has been shown to be decreased following administration of amphetamine or apomorphine (17,21). Yawning behavior after 4 weeks of streptozotocin (STZ)-induced diabetes in Wistar rats was significantly lowered when compared with their age-matched normal controls. Yawning behavior was not further diminished after an 8-week duration of diabetes mellitus; however, a significant recovery in yawning was seen by 20 weeks of diabetes. Yawning in rats after 20 weeks of STZ-induced diabetes mellitus is not significantly different from that seen in normal control rats. The results suggest that in STZ-induced diabetes of only 4 weeks duration a measurable change in the substrate for yawning has occurred.

Age-related changes in apomorphine-induced erections

Advancing age produces a noticeable and well-documented decline in erectile function in humans. The effects of aging on the ability of apomorphine to stimulate erection and yawning behavior in rats was studied in our bioassay for potency. At the age of seven months, rats failed to respond to the same dose of apomorphine which, just one month earlier, produced erections. Erectile function was then tested in thirty-two seven-month-old rats naive to apomorphine injections, and these rats also failed to respond. Experimentally naive rats of six months of age were then tested and apomorphine produced reliable erections. It is felt that an alteration in dopamine autoreceptor function may be occurring in the central nervous system of rats at approximately seven months of age rendering them incapable of responding to apomorphine with penile erections.

The characterization of a bio-assay of erectile function in a rat model

The investigation of biological phenomena in impotence using an animal system requires a determination of the erectile capabilities of the animal. Rats respond reliably to apomorphine by the exhibition of a phenomenon of erections and yawns. This property has been used to form the basis of a bio-assay of erectile integrity in the rat. We compared rats treated with placebo alone, sham operated rats, rats rendered surgically impotent and castrated rats with and without testosterone. Rats did not respond to placebo. The sham operated rats remained normal in all measured respects (2.66 erections/rat/30 minutes). Surgically impotent rats yawned normally but had no erections. Castrated rats did not have erections and had diminished yawning (3.21 yawns/rat/30 minutes vs. 7.7 for controls p less than .001) but responded normally after testosterone administration. The bio-assay is useful as a standard test of erectile function in the rat.

Metoclopramide decreases apomorphine-induced yawning and penile erection

Acute administration of metoclopramide, a dopamine (D2) antagonist, reduced both apomorphine-induced yawning and penile erections. Metoclopramide, prominent in clinical use as an effective antiemetic, has been shown to be associated with decreased erectile function in humans. Experimentally naive rats were given a standardized dose of apomorphine and one of a range of doses of metoclopramide. The study shows that metoclopramide decreases the erectile response to apomorphine and suggests that the erectile difficulties experienced in humans after metoclopramide treatment may be a result of interference with a central dopaminergic mechanism(s).