Abstract
This thesis covers papers published over an 11 year period from 1971-1983.
Research was undertaken to determine whether (i) prolactin was essential for normal
ovarian and testicular function and (ii) high levels of prolactin that occurred as
a clinical pathological state and physiologically in breast feeding and seasonal
anoestrous were implicated in the associated suppression of reproductive function.
To enable this research to proceed required reliable assay methods for
prolactin and gonadotrophins in all species studied and investigations into the
control of gonadotrophin secretion and ovarian function to provide the basic
background in which to explore the role of prolactin. The radioimmunoassays I
developed for prolactin and gonadotroph!"ns have been used in all investigations
reported in this thesis and have been utilized world-wide
In man it was thought that LHRH released both LH and FSH and it was used,
subsequently, in the treatment of hypogonadal states. The essential role of LHRH
in maintaining gonadotrophin secretion was shown by immunoneutralization studies in
the ewe while studies on the gonadotrophs subunits showed the commons subunit to
always be present in both pituitary and plasma while LHRH appeared to control
subunit formation. The essential role of pulsatile LH secretion in controlling
ovulation was also established and confirmed when ovulation was induced by
pulsatile hormone administration in anovulatory women and sheep
Both in vivo and in vitro studies indicated in women and other species that
prolactin was essential, with LH and FSH, for normal ovarian function.
Hyperprolactinaemia induced in the male rat suppressed gonadotrophin secretion by
increasing hypothalamic sensitivity to the negative feedback effects of gonadal
steroids. A similar increased sensitivity was shown in breast feeding women and
led to a major study on the causes of lactational infertility in women
This was the first large scale longitudinal study in breast feeding women and
it established that suppression of ovulation post partum was dependent on both
suckling frequency and duration. Resumption of ovulation only occurred when either
or both suckling parameters were reduced. Parallel studies showed the importance
of suckling patterns and the milk ejection reflex in establishing and maintaining
lactation and emphasized the need for on-going support for breast feeding mothers.
