Estrogen in a rebound experiment

The postmenopausal experiment

Veldhuis and colleagues studied 60 healthy postmenopausal women. They depleted endogenous estrogen with anastrozole and examined the rebound growth-hormone secretion that followed a short intravenous somatostatin infusion. The rebound was mediated by GHRH; estrogen depletion markedly reduced it.

The authors' conclusion gives low levels of endogenous estrogen a role in hypothalamic-pituitary growth-hormone regulation. The hormonal background becomes a participant whose contribution can be tested. I appreciate the reversal: the background becomes an experimentally visible contribution. Reducing it changes the response.

The finding also alters the emphasis of a menopause discussion. The interesting observation here concerns the effect of estrogen that was present. I would reserve more of the discussion for that remaining influence before reaching for a story about adding another hormone.

Following the rebound

The study's measured outcome was a GHRH-mediated growth-hormone rebound after somatostatin. The sequence matters because it describes responsiveness following a controlled intervention, rather than a claim about everyday energy, sleep or symptom relief.

I see the experiment as a way of asking a system a specific question. What does the rebound depend on? In this setting, depleting endogenous estrogen blunted it. That is a more precise conclusion than declaring the entire growth-hormone system deficient or restored.

There is no tesamorelin outcome to credit to this experiment. Its contribution is physiological: a demonstration that low endogenous estrogen levels participated in regulation of the measured rebound.

The result concerns a rebound response after an experimental infusion. Symptom relief would be a separate outcome.

Experiments in men

In 26 healthy older men, secretagogue experiments involving GHRH, somatostatin and GHRP-2 found that testosterone, estradiol and body mass index differentially controlled secretagogue-specific pulsatile growth-hormone secretion. Testosterone supplementation doubled GHRH-driven pulsatile output.

A separate study in 24 young men with experimentally induced hypogonadism found that testosterone and estradiol depletion did not affect growth-hormone secretion stimulated by L-arginine plus GHRH or L-arginine plus GHRP-2. The population and experimental conditions were different.

The postmenopausal rebound experiment has a defined setting and a persuasive result within it. The men's experiments make the wider physiology more interesting, without supplying a substitute answer for those women.

The next clinical question

A demonstration of hormonal influence opens a clinical question; it cannot choose a treatment on its own. A clinical study connecting the rebound response with a specified outcome in postmenopausal women would address the next clinical question. That is a question for future work, not a benefit measured in the rebound experiment.

Tesamorelin brings a modified GHRH analogue into the discussion. Its chemical design and its measured effects need their own examination.