The prolactin response to thyrotropin-releasing hormone does not distinguish teenaged males with hypogonadotropic hypogonadism from those with constitutional delay of growth and development.

We attempted to confirm the results of a previous study in which patients with hypogonadotropic hypogonadism (HH) could be readily distinguished from normal adolescents with constitutional delay of growth and development (CDGD) by their lower serum PRL responses to TRH. We compared the PRL responses to TRH of 13 teenaged males with HH to those of 14 teenaged males with CDGD. Although the mean maximum serum PRL concentration after TRH in HH patients (29.5 ng/ml) was significantly less (P less than 0.05) than that in the CDGD subjects (41.1 ng/ml), there was considerable overlap between the 2 groups. Seven of the 13 HH patients had peak serum PRL concentrations in response to TRH that were greater than 25 ng/ml, the lowest value in the CDGD subjects. These results suggest that a normal PRL response to TRH in a male who has delayed puberty does not exclude the diagnosis of HH, but that a subnormal response probably does support that diagnosis.

Evidence for abnormal heart induction in cardiac-mutant salamanders (Ambystoma mexicanum).

Homozygosity for simple recessive gene c in axolotl embryos results in the absence of a heartbeat. Gene c alters the morphology of the mutant anterior endoderm - the primary heart inductor.