Pulse observations
Evoking an LH pulse
A pulse can be evoked immediately. The experiment becomes interesting when the previous pulse stops determining the response.
The reset experiment
The study's title is wonderfully direct: Kisspeptin resets the hypothalamic GnRH clock in men. Thirteen healthy adult men received a single intravenous bolus of kisspeptin-10. An immediate LH pulse followed regardless of the timing of the preceding endogenous pulse. ‘Endogenous’ simply means arising within the body.
The authors interpreted the evoked pulse as reflecting roughly 17 minutes of sustained GnRH release. I relish that measured interval: how much activity lies behind the pulse observed in blood? It reaches beyond the statement that a peptide raised a hormone. The clock-reset interpretation concerns the organization of secretion over time.
My hesitation begins when ‘reset’ becomes a general claim about correcting someone's hormones. These were healthy adult men, and the finding concerns the hypothalamic pulse generator. The paper's intrigue survives perfectly well at that scale.
GnRH neurons
A mouse brain-slice experiment offers a more intimate view of how kisspeptin can excite GnRH neurons. Its response involved a phospholipase C and calcium pathway, closing potassium channels and opening non-selective cation channels. In that experimental preparation the electrical state of the neurons changed, allowing increased firing.
There is a pleasing difference between watching the hormone pulse in a person and investigating the cells that can help generate it. The brain-slice work gives a mechanism for excitement; the human experiment gives a temporal response. The argument convinces me because it connects both observations while retaining their different subjects.
Pulse frequency during infusion
Another study in healthy men using kisspeptin-10 reported an increase in LH pulse frequency from 0.7 to 1.0 pulses/h during continuous infusion. Its mean LH concentration also rose, from 5.2 to 14.1 IU/L. Frequency and concentration describe different features of the response, even when both change in the same experiment.
The clock-reset study and the infusion study therefore give me related, distinguishable questions. Can an intervention evoke a pulse irrespective of the last one? Can an exposure change how often pulses occur? A single high concentration would leave both questions largely unanswered.
Hypothalamic amenorrhea
In the kisspeptin-54 infusion study involving five women with hypothalamic amenorrhea, LH pulse counts rose from 1.6 to 5.0 per 8 h versus vehicle. Pulse secretory mass also increased. This is a different population from the healthy men in the reset experiment, and the intervention used the longer kisspeptin form.
The highest dose produced tachyphylaxis: a rapid decline in response during exposure. The restored pulses and the lost responsiveness must coexist in the explanation. Restored pulsatility makes the mechanism tangible; the loss of responsiveness complicates the ambition to sustain it. The fading-response essay follows that complication over a longer observation period.