When LH rose and lunch stayed the same
The food-intake experiment is a useful answer to the question “active at doing what?”
Food intake in women
In women with overweight or obesity, intravenous kisspeptin raised LH while leaving self-rated hunger and objectively measured food intake unchanged versus vehicle. The LH rise confirmed biological activity. The eating measurements answered the appetite question in this population.
For me, the disappointment is unusually useful. It closes off the convenient explanation that nothing happened because the peptide was inactive, while leaving the lack of an appetite effect in plain sight. A reproductive hormone response and a food-intake response were separate things to measure, and the experiment had the good sense to measure both.
The result also disciplines the language of potential. A connection with a hormone system can suggest an experiment. Once that experiment has measured food consumption, speculation has to make room for what was eaten. On appetite, I trust the food-intake measurement more than the metabolic speculation.
Anxiety measurements
A randomized crossover trial in 95 participants found a robust LH increase with kisspeptin-54, alongside no significant change in state anxiety, cortisol, blood pressure or heart rate versus placebo. It is another useful example of biological activity coexisting with unchanged outcomes elsewhere.
The absence of an acute change in those measured variables reassures me, within the confines of that experiment. Extending the reassurance to every exposure or every possible harm would outrun the observation. State anxiety is one outcome; blood pressure and heart rate are others. Their value comes from having actually been measured.
This is why the broad question of whether kisspeptin works quickly becomes several more interesting questions. A reply in LH gives the investigation somewhere to go. Each further outcome still has to answer for itself.
Receptor deletion in mice
Another experiment approached the metabolic question by removing the receptor. Adult female Kiss1r-knockout mice developed higher body weight and adiposity, impaired glucose tolerance and reduced energy expenditure. The study described a sexually dimorphic role for kisspeptin signaling in metabolism, with effects extending beyond gonadal estrogen.
That finding gives the metabolic hypothesis substance in a mouse model. The human food-intake experiment asked about adding kisspeptin to women with overweight or obesity. Deleting a receptor and administering a signal are different interventions, and food intake and energy expenditure are different measurements. Explaining the gap would require a sharper experiment. That prospect makes the pair worth my attention.
The reading list gathers these papers alongside the challenge studies. They reward being read as distinct experiments, each with its own question.