Prolactin, A Problem for Older Guys

January 09, 2017

Prolactin, A Problem for Older Guys 

 References: Jr of Endocrinology, Wikipedia, Nature Reviews

 Ever heard of prolactin? Bet not. From its name, you can surmise that it has something to do with helping lactation: "pro" - lactation. And that's just what it was discovered to do. It is secreted from the anterior pituitary in response to breast stimulation and helps milk let down. A mother can successfully breastfeed when she has her infant stimulate her nipple. That was figured out in the 1970s. Since then, we have found over 300 other functions in which it participates. 

 Prolactin isn't just made in the pituitary. It's made in lots of other places in much smaller amounts. It is quite similar in structure to growth hormone, nature being efficient with hormone design and building off one hormone to make more functions. It has 198 amino acids in it, so is a peptide hormone. As we dig deeper into biology, we are finding that the human metabolism is far more complicated than anything we ever imagined. Orgel's Third Law alludes to that: Nature is more complicated than you imagine, even when you take Orgel's Third Law into account. 

 Now, here's the rub. One of its functions is men's refractory period. The refractory period is the time after an orgasm during which a man is unable to be aroused again, cannot achieve an erection, and would rather read a book. That period is usually short in teen years (5 minutes) but gradually lengthens with age. With the right environment, it might only be a few minutes - hours in the 20-3os. By the age of 50-60, it can be a few days. 

Prolactin appears to be the mediator of that refractory period. As men age, their prostate gland enlarges, and the prostate also makes prolactin. That's where this week's study comes in. Ten men in Germany, who were otherwise healthy, had their prolactin measured and then shown erotic films and instructed to masturbate. This is difficult to turn into a double-blind trial, as you can imagine, so it was single-blinded and crossed over so that then subjects didn't know when they were getting a prolactin inhibitory drug called cabergoline. The cabergoline arm of the study was found to have significant reductions in prolactin, and enhanced all parameters of sexual drive (<0.05), function (<0.01), and perception of the length of the refractory period (< 0.01). 

The authors suggest that this is a possible route for study as we look into future effects on men's sexual health. Prolactin has over 300 actions in the body. It may play a role in brain cells making myelin, it probably mediates women's infertility while breastfeeding, in infants making surfactant in their lung, in immune tolerance of the mother's immune system to the fetus, the production of new brain cells... Orgel had it right. Nature is complicated, and we are just unpacking the surface. The interplay still to be discovered has a way to go.

 WWW. What will work for me? Well, it turns out cabergoline is now a drug on the market used for men's sexual health called Dostinex. And we are finding the measurement of prolactin starting to seep into standard blood assays. In my practice, my most used blood panel has it as a newly added feature, and I'm finding a lot of men and women have modestly elevated levels. I tell folks that a tiny percentage may have a pituitary tumor, but what to do with slightly elevated levels is still uncertain. There are web sites on how to lower it naturally for both men and women.

 Pop Quiz

1. Prolactin is a hormone that helps women breastfeed their infants. T or F?                    Answer:  T. That is what it was discovered to do ‪

2. Elevated prolactin plays a role in some men who have sexual dysfunction. T or F?                Answer: Again, true. ‪

3. Prolactin is secreted at the end of a sexual encounter and accounts for the sense of satisfaction afterward with the inability to become aroused again. T or F?           Answer:    True ‪

4. It is easy to measure prolactin. T or F?                       Answer:   ‪It is almost becoming routine, and lots of folks have modestly elevated levels. ‪

5. Prolactin causes cancer. T or F?                       Answer:  Whoa Nellie. Not so fast. It may be a growth factor for some cells, and cancers tend to shop around and find what growth factors they can use. Prolactin is similar in structure to growth hormone, but it isn't really a cancer causer.