Suppression by prolactin of the electrically induced erectile response through its direct effect on the corpus cavernosum penis in the dog

No evidence for prolactin's involvement in the post-ejaculatory refractory period

In many species, ejaculation is followed by a state of decreased sexual activity, the post-ejaculatory refractory period. Several lines of evidence have suggested prolactin, a pituitary hormone released around the time of ejaculation in humans and other animals, to be a decisive player in the establishment of the refractory period. However, data supporting this hypothesis is controversial. We took advantage of two different strains of house mouse, a wild derived and a classical laboratory strain that differ substantially in their sexual performance, to investigate prolactin's involvement in sexual activity and the refractory period. First, we show that there is prolactin release during sexual behavior in male mice. Second, using a pharmacological approach, we show that acute manipulations of prolactin levels, either mimicking the natural release during sexual behavior or inhibiting its occurrence, do not affect sexual activity or shorten the refractory period, respectively. Therefore, we show compelling evidence refuting the idea that prolactin released during copulation is involved in the establishment of the refractory period, a long-standing hypothesis in the field of behavioral endocrinology.

Effect of prolactin on penile erection: a cross-sectional study

Although elevated prolactin levels have been shown to inhibit penile erection, the relationship between prolactin and erection of the penile tip or base has not been extensively researched. We therefore investigated the prolactin's effects on erection of the penile tip and base, with a cross-sectional study of 135 patients with erectile dysfunction, based on scores of ≤21 on the International Index of Erectile Function-5. All patients were tested for nocturnal penile tumescence, blood pressure, serum glucose, total cholesterol, triglyceride, high-density lipoprotein, low-density lipoprotein, luteinizing hormone, follicle-stimulating hormone, prolactin, estradiol, testosterone, and progesterone. Univariate and multivariate analyses were used to assess the associations between prolactin levels and erection at the penile tip and base. We found no obvious relationship between erection time at penile tip and prolactin levels, but observed a negative correlation between base erection time and prolactin level (hazard ratio: −2.68; 95% confidence interval [CI]: −5.13–−0.22). With increasing prolactin concentration, multivariate analysis showed obvious reduction in base erection time among patients with normal Rigiscan results (hazard ratio: −3.10; 95% CI: −7.96–1.77; P < 0.05). Our data indicate that prolactin inhibits penile erection, particularly at the penile base. In addition, when the effective erection time of the penile base lasts longer than 10 min, prolactin has a more obvious inhibitory effect on penile base erection.

Effects of TNF-α on penile structure alteration in rats with hyperprolactinemia

This study aimed to investigate the effects of anti-tumor necrosis factor (TNF)-α antibody (Ab) on alteration of penile structure in the hyperprolactinemia (hyperPRL) rat model. HyperPRL was induced in 8-week-old male Sprague-Dawley rats by allografting anterior pituitary (AP) glands under the renal capsule (+AP rats). Rats implanted with cerebral cortex (CX) were used as sham control (+CX rats). At 6 weeks post implantation, rats received either a single intra-testicular dose of TNF-α Ab (12.5 μg/kg) or testosterone replacement (2 doses of testosterone enanthate [TE], 3 mg/kg), and they were sacrificed 1 week later. Blood and penile tissue was collected for analysis. Compared to +CX rats, the +AP group had lower serum testosterone concentration and neuronal nitric oxide synthase (nNOS) expression, but exhibited a higher ratio of collagen III/I in the corpus cavernosum. Smooth muscle content exhibited no significant changes. At 1 week post TNF-α Ab injection, the collagen III/I ratio in the +AP group was decreased, and the smooth muscle content and nNOS expression increased significantly. These findings were comparable to those observed in +AP rats receiving TE. Testicular TNF-α suppresses testosterone release, which in turn results in the erectile dysfunction (ED) seen in hyperPRL. Intra-testicular TNF-α Ab treatment is as effective as testosterone supplementation on penile structure normalization in the hyperPRL model.

Endocrine evaluation of erectile dysfunction

Erectile dysfunction is highly prevalent, affecting up to half of men in their 50-70s, and has been variably associated to a variety of causes including unhealthy lifestyles, such as smoking or overweight, or comorbidities such as hypertension, diabetes mellitus, and neurological disorders. General interest toward ED has exploded since the introduction of phosphodiesterase type 5 inhibitors-oral drugs that are widely accepted as the first line treatment in patients suffering from this conditions. In the last decade, the time lapse between first symptoms of sexual disorders and seeking of medical advice has greatly reduced. Unfortunately, none of the PDE5i has been proven curative, but rather acts as a symptomatic treatment. The availability of very active and safe drugs, however, diminished the space for diagnosis and search of etiological treatments. This is particularly true for the several endocrinopathies associated with ED. A number of epidemiological data support an inverse relationship between sexual health and testosterone levels, and it is well accepted that testosterone deficiency is a good marker of sexual and physical frailty. However, several other hormones, including LH, prolactin, TSH, and FT4 are involved in sexual functioning and should be investigated in a proper work-out of ED. Existing guidelines provide information almost entirely focusing on late-onset hypogonadism and therapeutic strategies; this mini-review aims to provide a wider spectrum of the diagnostic endocrine work-out of ED patients unrevealing the complexity of conditions, overt or subclinical, which can affect ED.