Could not understand why?? As it is the plasma levels of unbound steroid hormones is extremely low.... oh yes they recycle back to the liver for degradation and reformation of endogenous cholesterol....do they???
Once a hormone is secreted into the blood stream by an endocrine tissue, depending on their solubility, few, that are readily soluble in blood are transported free but most are bound to a specific plasma protein carrier, with the complex being disseminated to distant tissues. Plasma carrier proteins exist for all classes of endocrine hormones. Carrier proteins for peptide hormones prevent hormone destruction by plasma proteases. Carriers for steroid and thyroid hormones allow these very hydrophobic substances to be present in the plasma at concentrations several hundred-fold greater than their solubility in water would permit. Carriers for small, hydrophilic amino acid-derived hormones prevent their filtration through the renal glomerulus, greatly prolonging their circulating half-life.
Hormones need to be metabolically converted from their biologically active form into an inactive one. Inactivation can occur at various stages of hormone action. Peripheral inactivation (e.g. by liver enzymes) is required to ensure steady-state levels of plasma hormones as steroids are more or less continuously secreted into the bloodstream. Moreover, if a hormone is to act as a " chemical signal ", its half-life in the circulation must be limited, so that any change in secretion rate is immediately reflected by a change in its plasma concentration (particularly when secretion rates are decreased). But hormone inactivation can also occur in target tissues, notably after the hormone has triggered the relevant biological effects in order to ensure termination of hormone action.
The main site of peripheral steroid inactivation and catabolism is the liver, but some catabolic activity also occurs in the kidneys. Inactive hormones are mainly eliminated as urinary (mostly conjugated with sulphate and/or glucuronide derivatives) metabolites. Usually, steroids are eliminated once they have been inactivated (
i.e., they are not " recycled "). This elimination (e.g. as a urinary excretion products) requires conversion to hydrophilic compounds in order to ensure their solubility in biological fluids at rather high concentrations.
Glomerular filtrate has everything same as plasma except proteins. Steroid hormones , Thyroid hormones, Vitamins A, D, E, K all need protein as transporter to circulate in the blood.As there is no protein filtering into Glomerular filtrate, those Steroid hormones can not be filtered
Fingers crossed... Keep us posted.
