Progesterone

In blood only 1 to 15% of progesterone is in its unbound or biologically active form.  The remaining progesterone is bound to serum proteins.  Unbound progesterone enters the saliva via intracellular mechanisms, and the majority of progesterone in saliva is not protein-bound. (12)  Correlations obtained between plasma and salivary levels measured in the same subjects have generally been quite high. (13)

References

1. Tuckey, R.C. (2005). Progesterone synthesis by the human placenta.  Placenta, 26(4), 273-81.
2. Strott, C.A., Yoshimi, T., Lipsett, M.B. (1969).  Plasma progesterone and 17-hydroxyprogesterone in normal men and children with congential adrenal hyperplasia. J Clin Invest, 48(5), 930-39.
3. Soules, M.R., Clifton, D.K., Steiner R.A., et al. (1988). The corpus luteum: Determinants of progesterone secretion in the normal menstrual cycle. Obstet Gynecol, 71(5), 659-66.
4. Eppig, J.J. (2001). Oocyte control of ovarian follicular development and function in mammals.  Reproduction, 122(6), 829-38.
5. Veldhuis, J.D., Christiansen, E.C., Evans, W.S., et al. (1988).  Physiological profiles of episodic progesterone release during the midluteal phase of the human menstrual cycle: Analysis of circadian and ultradian rhythms, discrete pulse properties, and correlations with simultaneous luteinizing hormone release.  J Clin Endocrinol Metab, 66(2), 414-21.
6. Junkermann, H., Mangold, H., Vecsei, P., Runnebaum, B. (1982). Circadian rhythm of serum progesterone levels in human pregnancy and its relation to the rhythm of cortisol.  Acta Endocrinol, 101(1), 98-104.
7. Shah, C., Modi, D., Sachdeva, G., et al. (2005).  Coexistence of intracellular and membrane-bound progesterone receptors in human testis.  J Clin Endocrinol Metab, 90(1), 474-83.
8. Djebaili, M., Guo, Q., Pettus, E.H., et al. (2005).  The neurosteroids progesterone and allopregnanolone reduce cell death, gliosis, and functional deficits after traumatic brain injury in rats. J Neurotrauma, 22(1), 106-18.
9. Stein, D.G. (2008). Progesterone exerts neuroprotective effects after brain injury.  Brain Res Rev, 57(2), 386-97.
   
10. Wagner, C.K. (2006). The many faces of progesterone: A role in adult and developing male brain.  Front Neuroendocrinol, 27(3), 340-59.
11. Brown, S.L., Fredrickson, B.L., Wirth, M.M., et al. (2009).  Social closeness increases salivary progesterone in humans.  Horm Behav, 56(1), 108-111.)
12. Vining, R.F., McGinley, R.A. (1987). The measurement of hormones in saliva: Possibilities and pitfalls.  J Steroid Biochem, 27(1-3), 81-94.
13. Ellison, P.T. (1993). Measurements of salivary progesterone. In: Saliva as a diagnostic fluid, Malamud, D., Tabak, L., eds. Ann N Y Acad Sci, 694, 161-176.