When I was a beginning graduate student 41 yr ago it had been established that estrogen caused mammary duct growth; a combination of estrogen and progesterone
was required for lobule-alveolar development of the mammary glands; and prolactin and growth hormone were essential for mammary growth. In laboratory species exogenous prolactin, glucocorticoids, and estrogen would initiate secretion of milk provided the mammary glands had a well-developed lobule-alveolar system. It was not known with certainty that progesterone inhibited the process. For some species, prolactin and thyroxine had been shown to stimulate lactation, while glucocorticoids suppressed lactation. Definitive roles for growth hormone and insulin during lactation had not been established. Studies of hormonal control of mammary growth and function in cattle were few. In vitro methods to study hormonal regulation of the mammary glands were in their infancy.

A historical perspective of hormonal regulation of mammary growth and function was requested of me— a daunting task when one considers the tens of thousands of publications on this subject, which began before 1900. However, the recent commentary of Professor R. H. Foote (41) rightly encourages us to become better students of history in order to more critically evaluate and understand data currently being generated. So a
few historical and classical bits of information with selected references that summarize the state of my knowledge before 1958, the year I entered graduate school, are presented in the first section of this report. Remember, the scientific literature that precedes the advent of computer searches of the literature is extensive. So go to the library and become acquainted with some of the old classics cited in these reviews because they are
a basis for our current knowledge of the field. The objective of the remainder of this paper is to provide an overview of some the discoveries made since 1958 regarding
interactions among major hormones that control mammary growth and lactation. Selected reviews that will expose the reader to many additional highquality original manuscripts are presented. Many of these discoveries were based on development of new technologies such as in vitro methods to culture mammary slices and cells; radioimmunoassays for measurement of concentrations of hormones in blood and milk;
objective methods to quantify mammary cell numbers, chemical components of milk, and number and affinity of hormone receptors; and most recently, development
of methods to determine molecular mechanisms of how hormones turn on specific genes.

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