A.A. van der Gugten

Radioimmunoassay of rat prolactin: Prolactin levels in plasma of rats with spontaneous pituitary tumours, primary oestrone-induced pituitary tumours or pituitary tumour transplants

In old female rats a close correlation was observed between detecting elevated prolactin levels in the circulation and the presence of spontaneous pituitary tumours on the one hand and mammary tumours on the other hand. Weekly oestrone-cholesterol pellet implantation in a group of 4 orchidectomized rats resulted in a rapid rise in prolactin plasma levels, indicative of very high secretion rates of this hormone by the pituitary gland as a consequence of oestrone stimulation. These high rates of secretion apparently were maintained for over 110 days without great fluctuations. Between day 110 and day 150 a further and more or less progressive increase of plasma prolactin was found to occur, which probably was related to the progressive increase in weight of the pituitary occurring around this time in this strain of rats under this regimen. Rats bearing transplants of oestrone-induced pituitary tumours and in which one oestrone-cholesterol pellet was implanted monthly showed great variations in prolactin output in response to the oestrone stimulus as well as great variations in the rate of growth of the grafts. The majority of the grafts, however, responded with a maximum outflow of prolactin reflected in high plasma values around 2 weeks after implantation of the oestrone. The findings suggested that an extreme hyperfunction that will maintain high prolactin levels over long periods of time was not primarily caused by implantation away from the restraining influence of the hypothalamus, but was consequent to relatively high doses of oestrogen.

Effect of pituitary tumours and grafts on plasma prolactin levels

Abstract Using radioimmunoassays the influence on the plasma prolactin levels of oestrone and pituitary isografts in mice and of oestrone, pituitary isografts and chloorpromazine in rats, have been observed in a number of experiments. Suggestive evidence is given for the existence of a Prolactin Releasing Agent in Rats.

Presence of immunoreactive growth hormone and prolactin in the ovine pineal gland

Abstract: The use of antisera raised against bovine growth hormone (GH) and ovine prolactin (PRL) enabled the detection of related immunoreactive (ir) sequences of proteins in ovine pineal tissue. The isolation of PRL‐like ir‐material was accomplished using a 0.25 M ammonium sulphate (pH 5.5) extraction followed by ethanol precipitation, whereas the resulting 2.0 M ammonium sulphate (pH 7.0) precipitate contained a GH‐like immunoreactivity. Gel chromatography of the GH‐like immunoreactivity (Sephadex G‐100) indicated the presence of several GH‐like fragments ranging in the Mr range of 7,000 to 55,000. Analyses of the PRL‐like ir‐material found in pineal tissue on HPLC using a TSK 545‐DEAE column led to the resolution into a single peak of immunoreactivity. A single peak of activity was also observed following chromatofocusing and hydrophobic interaction chromatography of the ir‐peak from the TSK 545‐DEAE column. The PRL‐like ir‐material inhibited the binding of [125I]ovine PRL‐S14 to anti‐ovine PRL antibodies without showing an affinity for binding to anti‐rat PRL or anti‐bovine GH antibodies. Scatchard analysis of the binding of pineal PRL‐like ir‐material and pituitary ovine PRL‐S14 to liver membranes from day‐20 pregnant rats revealed similar affinity constants (Ka of 4.7 ± 0.2 × 109 M‐1). In addition, the replication of Nb 2 Node rat lymphoma cells was stimulated by pineal PRL‐like ir‐material, an effect known to be specific for lactogenic hormones. The pineal PRL‐like immunoreactivity appeared on sodium dodecyl sulfate polyacrylamide gels as a single major band of Mr 24,000. The functional status of PRL‐and GH‐like ir‐material in the ovine pineal remains to be determined, but evidence is presented that the overall protein synthesis rate of the rat pineal responded to circulating concentrations of PRL.

Hierarchies in control

The living cell functions by virtue of an enormous number of different processes. It is one of the most difficult challenges of modern biology to elucidate how all those processes are coordinated quantitatively so as to lead to a viable system with optimal responses to various changes in the environment. The biochemical and biophysical processes of the living cell do not constitute a network with random connections. In this paper we shall discuss that cell function is organized in hierarchical substructures. We will briefly touch on the topics of (i) metabolic control and regulated gene expression, (ii) time dependent metabolism in intact yeast cells, and (iii) metabolite channelling.

Control theory of cell metabolism: towards more realistic "non-ideal" systems.

Metabolic Control Analyses have led to significant advances in understanding the control of cell metabolism. However, the classical theory does not address all complex cases of the organization of cellular metabolism. Here the control theory is extended to include (i) pathways with high enzyme concentrations and moiety conservation and (ii) metabolic channelling in general. The new theory descends the microlevel of elemental steps into the reaction cycle of the enzymes and turns back to the macrolevel of complete enzyme reactions. We showed how the elemental control coefficients are related to the traditional flux control coefficients of the enzymes. We derived what the sums of the enzyme control coefficients are equal to in various non-ideal cell pathways.

Object Oriented Simulation of Metabolic Processes

Simulation of metabolic processes in cells is usually done by solving sets of coupled differential equations (using software systems like for instance SCoP1 or MLAB2). Each equation represents the change per unit of time in the concentration of a certain metabolite or other substance. Such a rate of change depends on the rates of all chemical reactions that produce or consume that substance. In the modeling and simulation approach we present here, we focus on the essential independence of the underlying reactions.