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RACHMIEL LEVINE
edge of the molecular geography of the cell is still so rudimentary it
may only be possible, for some time to come, to describe hormonal action
at the level of cell architecture or cell component.
The term "function" of a hormone should be reserved for the deductions made from the observations of effects of administration and removal of hormones, as to the role of the particular hormone in the
economy of the organism and its homeostatic adjustments. The chemical
nature of the known hormones does not throw any light on the mode of
their action. It ranges from comparatively simple amines (adrenaline)
and amino acids (the thyroid group) through peptides (posterior pituitary) and steroids (adrenal cortex and gonads) to proteins of varying
complexity (insulin, anterior pituitary, etc.). We may therefore assume
that their intimate modes of action at the chemical level would show at
least a similar degree of variability. However, from a biological standpoint, the hormones form a more uniform group of materials—that of
humoral signal systems. They serve to integrate organ and cell functions
in a manner which appears goal-directed in respect to the organism
as a whole, especially in its adaptation to induced changes.
In the test tube the rates of enzymatic processes depend upon concentrations of substrate and catalyst, inorganic ion strengths, pH, substrate removal, etc. In the cell the innumerable chemical reactions are
in addition controlled by structural characteristics at the submicroscopic
level—the macromolecular complexes, organelles, and the resulting multitude of surfaces. More and more attention is being paid to these
geometrical aspects of biological chemistry, despite the difficulties in
approach. In a multicellular organism, it would seem likely that it is
the role of the hormones (as it is of the peripheral nervous system) to
bring about, reversibly, subtle changes in submicroscopic form and thus
to trigger a change in functional direction as well as in rate of a process.
This viewpoint is supported in part by the repeated observations that it
becomes more and more difficult to elicit a hormonal effect as one
proceeds from the whole organism to isolated organs, tissue slices,
homogenates, and subcellular preparations. A certain degree of morphological intactness seems necessary for hormonal (and drug) actions. The
gun needs to be at least partially assembled for the demonstration of the
action of the trigger.
These general considerations, however sketchy, are intended to serve
as an introduction to a more detailed exposition of our present state of
knowledge concerning the mode of action of several of the hormones.
The selection was dictated by the type of information already available,
and for the purpose of illustrating a variety of approaches. Considera-
RACHMIEL LEVINE
edge of the molecular geography of the cell is still so rudimentary it
may only be possible, for some time to come, to describe hormonal action
at the level of cell architecture or cell component.
The term "function" of a hormone should be reserved for the deductions made from the observations of effects of administration and removal of hormones, as to the role of the particular hormone in the
economy of the organism and its homeostatic adjustments. The chemical
nature of the known hormones does not throw any light on the mode of
their action. It ranges from comparatively simple amines (adrenaline)
and amino acids (the thyroid group) through peptides (posterior pituitary) and steroids (adrenal cortex and gonads) to proteins of varying
complexity (insulin, anterior pituitary, etc.). We may therefore assume
that their intimate modes of action at the chemical level would show at
least a similar degree of variability. However, from a biological standpoint, the hormones form a more uniform group of materials—that of
humoral signal systems. They serve to integrate organ and cell functions
in a manner which appears goal-directed in respect to the organism
as a whole, especially in its adaptation to induced changes.
In the test tube the rates of enzymatic processes depend upon concentrations of substrate and catalyst, inorganic ion strengths, pH, substrate removal, etc. In the cell the innumerable chemical reactions are
in addition controlled by structural characteristics at the submicroscopic
level—the macromolecular complexes, organelles, and the resulting multitude of surfaces. More and more attention is being paid to these
geometrical aspects of biological chemistry, despite the difficulties in
approach. In a multicellular organism, it would seem likely that it is
the role of the hormones (as it is of the peripheral nervous system) to
bring about, reversibly, subtle changes in submicroscopic form and thus
to trigger a change in functional direction as well as in rate of a process.
This viewpoint is supported in part by the repeated observations that it
becomes more and more difficult to elicit a hormonal effect as one
proceeds from the whole organism to isolated organs, tissue slices,
homogenates, and subcellular preparations. A certain degree of morphological intactness seems necessary for hormonal (and drug) actions. The
gun needs to be at least partially assembled for the demonstration of the
action of the trigger.
These general considerations, however sketchy, are intended to serve
as an introduction to a more detailed exposition of our present state of
knowledge concerning the mode of action of several of the hormones.
The selection was dictated by the type of information already available,
and for the purpose of illustrating a variety of approaches. Considera-