Interplay of antiferromagnetic coupling in copper/permalloy combination multilayers

Heitmann S, Hütten A, Hempel T, Schepper W, Reiss G, Alof C. Interplay of antiferromagnetic coupling in copper/permalloy combination multilayers. In: Journal of Applied Physics. JOURNAL OF APPLIED PHYSICS. Vol 87. AMER INST PHYSICS; 2000: 4849-4851.The evolution of the giant magnetoresistance (GMR) effect in sputtered combination multilayers (CMLs) of type Py-1.8nm//{(Cu-1.8nm/Py-1.6nm)(N)/(Cu-0.9nm/Py-1.6nm)(N)}(y) with Py (permalloy=Ni81Fe19) has been investigated at room temperature. It is shown that the GMR characteristic of these CMLs can be phenomenologically predicted, if the physical properties are known, i.e., the GMR effect amplitude, double layer conductance, and bilinear and biquadratic antiferromagnetic exchange coupling constants of the two underlying {Cu/Py}(N) base systems at the first (Cu-0.9nm) and second (Cu-1.8nm) antiferromagnetic coupling maximum (AFCM). The GMR characteristic of the simplest CML with N = 1 is, e.g., determined by averaging the bilinear and biqua dratic exchange coupling constants of the two base systems. The GMR characteristics of CML with N greater than or equal to 2 are a superposition of that of the underlying {Cu/Py}(N) base systems weighted by the fraction of the corresponding double layer conductance. Furthermore, it is demonstrated that the CMLs are interesting from an application point of view since they combine the temperature stability of the underlying {Cu/Py}(N) base system at the second AFCM with a larger GMR effect amplitude. (C) 2000 American Institute of Physics. [S0021-8979(00)57908-0]

Somatostatin Receptor Expression in GH-Secreting Pituitary Adenomas Treated with Long-Acting Somatostatin Analogues in Combination with Pegvisomant

Background: Growth hormone secreting pituitary adenomas (somatotroph adenoma) predominantly express somatostatin receptors (SSTRs) subtypes 2 and 5. Higher SSTR2 expression on somatotroph adenomas results in a better response to somatostatin analogues (SSAs), which preferentially bind, but also down regulate, SSTR2. The effect of the combined treatment with SSAs and the GH receptor antagonist pegvisomant (PEGV) on SSTR expression in somatotroph adenomas is currently unknown. Aim of the Study: To assess SSTR2 and SSTR5 expression in three groups of somatotroph adenomas: drug-naive, treated with long-acting (LA) SSA monotherapy, or LA-SSA/PEGV combination therapy before surgery. Additionally, we evaluated the required PEGV dose to achieve IGF-I normalization in relation to the SSTR expression. Materials and Methods: At our Pituitary Center Rotterdam, we selected acromegalic patients who underwent transsphenoidal neurosurgery. All patients were eventually treated with LA-SSA/PEGV combination therapy during their medical history. SSTR2 and SSTR5 expression in somatotroph adenomas tissues was determined using immunohistochemistry. Results: Out of 39 somatotroph adenoma tissue samples, 23 were drug-naive, 9 received pre-treatment with LA-SSA and 7 LA-SSA/PEGV combined treatment. SSTR2 expression was significantly higher in treatment-naive compared to combined treatment somatotroph adenomas (p = 0.048), while SSTR5 expression did not differ. Noteworthy, SSTR2 expression in naive somatotroph adenoma tissues was inversely correlated to the required PEGV dose to achieve IGF-I normalization during post-surgical medical treatment (\u3c1 = -0.538, p = 0.024). Conclusion: In our specific cohort, the SSTR2 expression is lower in patients pre-treated with LA-SSA/PEGV compared to the drug-naive acromegalic patients. Additionally, the SSTR2 expression in treatment naive somatotroph adenoma tissues was inversely correlated with the required PEGV dose to achieve IGF-I normalization