11.     The Anterior Pituitary:

The pituitary has a portal circulation, which makes it vulnerable to hypotension, as in Sheehan’s syndrome (See MCQ 8, question 11). 

It does not produce GnRH, which comes from the hypothalamus in pulsatile fashion to stimulate production of FSH and LH.

Oxytocin comes from the posterior pituitary.

Prolactin is produced by the anterior pituitary.

But the control mechanism is unusual.

It is a matter of inhibition by the Prolactin Inhibiting Factor - PIF.

Left to its own devices, the pituitary would churn out prolactin and we would all be liable to galactorrhoea.

The PIF keeps things on an even keel.

Evidence points to dopamine being the PIF.

Hence the use of dopamine agonists to suppress hyperprolactinaemia and prolactinomas.

And the association between drugs which reduce dopamine levels (phenothiazines, methyl dopa, reserpine etc.) and hyperprolactinaemia.

No specific trophic hormone has been identified and the major control mechanism is believed to be the above. 

Thyrotropin releasing hormone, TRH, produced by the hypothalamus, triggers release of thyroid stimulating hormone, TSH, from the pituitary. 

In hypothyroidism, TRH levels rise as the hypothalamus tries to kick the pituitary into producing more TSH to get the thyroid to work properly. 

TRH has a trophic effect on prolactin release and may be the explanation for the elevated prolactin levels which can be found in hypothyroidism.