[Pet biology 301: Phenotype : Pethood Gonadal Dormancy (PHGD)]

Pethood Gonadal Dormancy (PHGD) explains why petgirls are by nature sterile.

Because SRY prevents male PH-phenotypes to be conceived only females are affected.

The HPG axis is a term used by scientists to refer to the hypothalamus, pituitary gland, and gonadal glands as a whole because they often act in concert. The hypothalamus secretes Gonadotropin-Releasing Hormone (GnRH) which triggers the pituitary gland to release Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) which triggers the gonal glands to produce estrogen and testosterone. Progesterone is a progestogen. The progestogens are one of three types of sex hormones; the other two are estrogens and androgens (like testosterone).

FSH and LH work in tandem. While FSH ensures pubertal maturation LH triggers ovulation in females. In most mammals, including humans, a feedback loop between LH, estrogen, and progesterone turned ovulation into an autonomous process.

Schematically the loop goes like this: estrogen signals an egg is ready, the hypothalamus triggers the release of LH, progesterone signals the empty follicle as the egg is released. If this leads to a pregnancy, the cycle is stopped. If not, the loop starts again.

In most mammals estradiol boots up the feedback loop. Humans, however, need estroxin for this. However, for PH-phenotypes this feedback loop doesn’t seem to work. Taking into account the estroxin link in humans, some scientists point to PTX as “the culprit” for PHGD but research is still ongoing.

For PH-phenotypes with a pregnancy wish, there is good news. Administering LH manually seems to trigger ovulation.