THE STIMULUS TO HYPERTROPHIC GROWTH
107
hypertrophy following partial hepatectomy depends on the presence of
cortisone and pituitary growth hormone together. This is not to say that
the stimulus to hypertrophic growth comes from the secretion of these
substances, although they may be involved in the control of normal growth
of the liver. Growth hormone and other hormones appear to be involved
in the process of protein synthesis (Korner, 1962; Wagle, 1963).
C. Attempted Demonstration of a Humoral Stimulus
If the stimulus to hypertrophic liver growth is humoral in nature, then
the serum of animals should contain either inhibitors or stimulators of liver
growth. There have been many attempts to demonstrate this experimentally
in rats. One approach has been to perform a partial hepatectomy on one
rat of a parabiotic pair, or two rats of a parabiotic triplet, and to look for
a hypertrophic response in the liver of the intact partner. Bucher
et al. (1951), Christensen and Jacobsen (1949), Van Lanker and
Sempoux (1959), and Wenneker and Sussman (1951) all found an elevated
mitotic index in the intact liver of the parabiotic partner. They used small
numbers of parabions, and their controls were single rats. Van Lanker and
Sempoux, in a preliminary experiment, found no difference between the
mitotic index in the liver of a single rat and that in the partner of a shamoperated parabion. Islami et al. (1961) found a decreased mitotic index
in the liver remnant of a partially hepatectomized parabion compared with
a partially hepatectomized single rat, but they found no response in the
liver of the intact parabiotic partner. Rogers et al. (1961), using many
parabiotic pairs and triplets and parabiotic controls, could find no increased
mitotic activity in the liver of the intact rat in parabiosis to either one or
two partially hepatectomized rats. Fisher et al. (1963) found a slightly
elevated mitotic index in the liver of the parabiotic partner of a shamoperated rat. They attributed the different results of earlier workers to this
effect, although the changes reported before were very much larger than
the changes they found. Their conclusion was that liver hypertrophy does
not involve a humoral stimulus. More recently, the same group reported
finding an inhibition of liver hypertrophy in the remnant of one partially
hepatectomized rat parabiosed to two intact rats (Pechet et al. y 1962).
Alston and Thompson (1963) used a method of temporary parabiosis with
which labeled erythrocytes became completely distributed in the circulations of two animals within 10 min after injection into one of them. They
could find no mitotic response in the liver of an intact rat parabiosed to a
rat which had been partially hepatectomized 30 min before.
The most convincing evidence of a humoral stimulus to liver hypertrophy
comes from two recent reports of an elevation of mitotic activity in autografts of liver after partial hepatectomy (Leong et al., 1964; Virolainen,
107
hypertrophy following partial hepatectomy depends on the presence of
cortisone and pituitary growth hormone together. This is not to say that
the stimulus to hypertrophic growth comes from the secretion of these
substances, although they may be involved in the control of normal growth
of the liver. Growth hormone and other hormones appear to be involved
in the process of protein synthesis (Korner, 1962; Wagle, 1963).
C. Attempted Demonstration of a Humoral Stimulus
If the stimulus to hypertrophic liver growth is humoral in nature, then
the serum of animals should contain either inhibitors or stimulators of liver
growth. There have been many attempts to demonstrate this experimentally
in rats. One approach has been to perform a partial hepatectomy on one
rat of a parabiotic pair, or two rats of a parabiotic triplet, and to look for
a hypertrophic response in the liver of the intact partner. Bucher
et al. (1951), Christensen and Jacobsen (1949), Van Lanker and
Sempoux (1959), and Wenneker and Sussman (1951) all found an elevated
mitotic index in the intact liver of the parabiotic partner. They used small
numbers of parabions, and their controls were single rats. Van Lanker and
Sempoux, in a preliminary experiment, found no difference between the
mitotic index in the liver of a single rat and that in the partner of a shamoperated parabion. Islami et al. (1961) found a decreased mitotic index
in the liver remnant of a partially hepatectomized parabion compared with
a partially hepatectomized single rat, but they found no response in the
liver of the intact parabiotic partner. Rogers et al. (1961), using many
parabiotic pairs and triplets and parabiotic controls, could find no increased
mitotic activity in the liver of the intact rat in parabiosis to either one or
two partially hepatectomized rats. Fisher et al. (1963) found a slightly
elevated mitotic index in the liver of the parabiotic partner of a shamoperated rat. They attributed the different results of earlier workers to this
effect, although the changes reported before were very much larger than
the changes they found. Their conclusion was that liver hypertrophy does
not involve a humoral stimulus. More recently, the same group reported
finding an inhibition of liver hypertrophy in the remnant of one partially
hepatectomized rat parabiosed to two intact rats (Pechet et al. y 1962).
Alston and Thompson (1963) used a method of temporary parabiosis with
which labeled erythrocytes became completely distributed in the circulations of two animals within 10 min after injection into one of them. They
could find no mitotic response in the liver of an intact rat parabiosed to a
rat which had been partially hepatectomized 30 min before.
The most convincing evidence of a humoral stimulus to liver hypertrophy
comes from two recent reports of an elevation of mitotic activity in autografts of liver after partial hepatectomy (Leong et al., 1964; Virolainen,