# A question of capacity at Hormone Consultants

> Hormone Consultants explores kisspeptin as a question put to a hormone system: which responses reveal capacity, and which questions remain open.

**Hormone systems under challenge**

A consultation starts with a question. The provocation studies pull me in: can this hormone system answer?

## A failed kisspeptin challenge

A hormone experiment can be useful when the expected rise never arrives. In a study of patients with abiding idiopathic hypogonadotropic hypogonadism, [a kisspeptin bolus failed to provoke the GnRH-induced LH response that it reliably triggered in healthy men](https://pubmed.ncbi.nlm.nih.gov/25226293/). The authors used that difference to investigate the functional capacity of the GnRH neuronal network.

That is an unusually interesting job for a peptide. Before this paper, raising hormone concentrations seemed like the main attraction of kisspeptin to me. Here the appeal lay in asking something of a system and learning from its inability to respond. The study’s defined patient group matters just as much as the substance used to challenge it.

I hear a demand for careful questioning in the name Hormone Consultants, with the reply examined before anyone rushes to conclusions. These experiments give that thought a concrete subject: the capacity of a reproductive hormone system to respond. A failed challenge deserves as much curiosity as a spectacular rise.

## The receiving machinery

The case for paying attention to that machinery begins with genetics. [Loss-of-function GPR54 mutations were associated with failure of puberty in humans, and knockout mice reproduced the phenotype](https://pubmed.ncbi.nlm.nih.gov/14573733/). GPR54 is also called KISS1R, the receptor for kisspeptin. A response requires a working relationship between a signal and the system receiving it.

At a closer scale, [kisspeptin excited GnRH neurons in mouse brain-slice experiments through a calcium-dependent process involving several ion channels](https://pubmed.ncbi.nlm.nih.gov/18483150/). GnRH means gonadotropin-releasing hormone. The experiments concern the activity of nerve cells, a very different observation from the blood LH response in the human challenge study.

I like the distance between those observations. The mouse experiment gives the proposed conversation a physical mechanism; the human experiment asks whether the network can actually answer in a particular disorder. Neither observation makes the other redundant.

## Three questions to pursue

[Responsiveness accompanied reactivation of the reproductive axis in a cohort of men whose congenital disorder had reversed](https://pubmed.ncbi.nlm.nih.gov/27214398/). That result starts the essay on [kisspeptin as a functional probe](/challenge), where the question is whether a response can help characterize the state of a system.

The [amenorrhea experiments](/amenorrhea) ask a different question about stimulation over time. The [food-intake essay](/appetite) leaves reproductive outcomes behind and asks why an active hormone signal could coexist with unchanged eating measurements. I’m drawn to both because they put limits on the easy verb “works.” Works at doing what?

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Hormone Consultants houses my questions for published research, with no consulting business behind the name and no medical advice in these essays.