Sex hormone binding globulin (SHBG) is a glycoprotein possessing high affinity binding for 17 beta-hydroxysteriod hormones such as testosterone and oestradiol. It is probably synthesized in the liver, plasma concentrations being regulated by, amongst other things, androgen/oestrogen balance, thyroid hormones, insulin and dietary factors, it is involved in transport of sex steroids in plasma and its concentration is a major factor regulating their distribution between the protein-bound and free states. Its detailed role in the delivery of hormones to target tissues is not yet clear. Plasma SHBG concentrations are affected by a number of different diseases, high values being found in hyperthyroidism, hypogonadism, androgen insensitivity and hepatic cirrhosis in men. Low concentrations are found in myxoedema, hyperprolactinaemia and syndromes of excessive androgen activity. Concentrations are also affected by drugs such as androgens, oestrogens, thyroid hormones and anti-convulsants. Measurement of SHBG is useful in the evaluation of mild disorders of androgen metabolism and enables identification of those women with hirsutism who are more likely to respond to oestrogen therapy. Testosterone:SHBG ratios correlate well with both measured and calculated values of free testosterone and help to discriminate subjects with excessive androgen activity from normal individuals.

https://journals.sagepub.com/doi/pdf/10.1177/000456329002700603

Sex hormone binding globulin: origin, function and clinical significance.

Intermediate trophoblast: a distinctive form of trophoblast with specific morphological, biochemical and functional features

Plasma corticotrophin-releasing factor (CRF) in normal pregnancy.

It is well established that pregnancy early in life reduces the
 risk of breast cancer in women and that this effect is universal This
 phenomenon of parity protection against mammary cancer is also observed
 in rodents Earlier studies have demonstrated that short-term
 administration of estradiol (E) in combination with progesterone mimics
 the protective effect of parity in rats In this study, the lowest
 effective E dosage for preventing mammary cancer was determined Rats
 were injected with N-methyl-N-nitrosourea
 at 7 weeks of age; 2 weeks later, the rats were subjected to sustained
 treatment with 20 μg, 100 μg, 200 μg, or 30 mg of E in silastic
 capsules for 3 weeks Treatments with 100 μg, 200 μg, and 30 mg of
 E resulted in serum levels of E equivalent to those of pregnancy and
 were highly effective in preventing mammary cancer E treatment (20
 μg) did not result in pregnancy levels of E and was not effective in
 reducing the mammary cancer incidence In another set of experiments,
 we determined the effect of different durations of E with or without
 progesterone treatments on mammary carcinogenesis These experiments
 indicate that a period as short as one-third the period of gestation is
 sufficient to induce protection against mammary carcinogenesis The
 pioneering aspect of our study in contrast to long-term estrogen
 exposure, which is thought to increase the risk of breast cancer, is
 that short-term sustained treatments with pregnancy levels of E can
 induce protection against frank mammary cancer

https://www.pnas.org/content/pnas/98/20/11755.full.pdf

Short-term exposure to pregnancy levels of estrogen prevents mammary carcinogenesis

Effect of pregnancy and lactation upon infection.

Pregnancy specific β1 (PSβG) has been identified in vitro in trophoblast cultures and in vivo, using transmission electron microscopy, in the syncytiotrophoblast, PSβG may, like other pregnancy proteins, have immunosuppressive properties.

Pregnancy specific beta1-glycoprotein--a product of the syncytiotrophoblast.

A serial study of pregnancy proteins in primigravidae

Placental protein 5 (pp5): development of a radioimmunoassay and measurement of circulating levels in normal pregnancy

Sensitive radioimmunoassays for the placental proteins PP5 and SP1 were used to investigate possible ectopic synthesis of these proteins by breast tumors. Elevated serum levels of the proteins were found in a small proportion of patients who had undergone mastectomy for malignant tumors, but little useful information on tumor spread could be gained from such measurements. In two patients with elevated pre-operative serum PP5, the levels fell to normal upon resection of the tumor, suggesting that PP5 may be a product of the tumor. PP5 and SP1 were found to be present in the majority of homogenates of malignant and benign breast lesions; the highest concentrations of SP1 were found in malignant tumors, whereas with PP5, especially high levels were found in cases of simple cystic disease.

H. Bohn

Papers

Pregnancy specific beta1-glycoprotein--a product of the syncytiotrophoblast.

A serial study of pregnancy proteins in primigravidae

Placental protein 5 (pp5): development of a radioimmunoassay and measurement of circulating levels in normal pregnancy

Detection of placental protein five (PP5) and pregnancy-specific glycoprotein (SP1) in benign and malignant breast disease.

Placental protein 5 (pp5) in complicated pregnancies